Just a hunch, but I suspect maybe the reason the line wasn't successful was the lack of Thomas trains?
I know that's odd and ironic considering at the same time, Trackmaster era Thomas was still more or less Plarail compatible (heck, I owned adapters officially packed into a set of the brown track to connect it to Plarail/Tomica blue) meaning in theory one could use the Tomica sets as expansions to a Thomas layout (and vice versa), but the thing is, given how Tomica World morphed into Motor Road and Rail, dispensing with the Japanese models in favour of Thomas, my theory is that people in Europe and the US (at least, the majority of people buying sets for their kids) wanted Thomas, as that's what the kids wanted.
Therefore it's my theory that Tomica/Plarail simply couldn't compete against Thomas both times, as for better or worse, people wanted trains they recognise as opposed to awesome, but outside of Japan relatively obscure models, and by the time they got to start selling the Plarail system in the West again, they'd lost the lucrative Thomas license that would have kept the Plarail line selling - Again, make of that what you will, personally I think there was ways they could have improved their marketing, such as making the origins of the trains more clear with a few facts about the model on the box like the Japanese versions (interesting for the kids/adults), maybe selling some of the Japanese steam models as steam trains are universally popular (plus, Hiro in Thomas has given Japanese steam some recognition worldwide), making a few unique 'world' trains like Tomica World had, such as the TGV, Eurostar, Amtrak and HST to add some recognisable stock in with the Japanese (I mean, they could have updated, had an Acela, newer TGV or even a UK Javelin as that was based on the 400 Series so it wouldn't have been too hard to recreate), and perhaps market Tomica as more of an integrated model system that can be both a toy and a long-term hobby (Hint, look at how Hornby et al markets, and push for that).
Same goes for the Tomica cars, because they were never sold in the Hot Wheels single pack format in the UK or Europe I don't think they ever stood a chance against the entrenched Western brands, in spite of being (IMHO) considerably better models in almost all aspects.
It is a shame, as somehow I'm not sure if we'll ever see Plarail again in the West as I think Tomy have been spooked out of a re-release by the popularity of Trackmaster - That said, considering the current direction of Trackmaster one has to wonder wether Tomy may take the opportunity to return again, given that many people preferred (at least, of the people I know) the stuff that was fully compatible across Plarail and G1 Trackmaster track as opposed to the newer stuff that seems only to work with current Trackmaster tracks and nothing else. Honestly though, without the Thomas licence (and let's face it, Mattel aren't likely to give that back to Tomy for the West), I don't see it happening, but hey, these last few years have been so screwy, stranger things have, and could well happen - Should the Plarail revival ever occur, you'd better belive ill be posting pics of a trolley load of goodies from my local Smyths, Toys R Us or whoever has stock, because I'll be there faster than they can say 'Plarail' lol
I know that's odd and ironic considering at the same time, Trackmaster era Thomas was still more or less Plarail compatible (heck, I owned adapters officially packed into a set of the brown track to connect it to Plarail/Tomica blue) meaning in theory one could use the Tomica sets as expansions to a Thomas layout (and vice versa), but the thing is, given how Tomica World morphed into Motor Road and Rail, dispensing with the Japanese models in favour of Thomas, my theory is that people in Europe and the US (at least, the majority of people buying sets for their kids) wanted Thomas, as that's what the kids wanted.
Therefore it's my theory that Tomica/Plarail simply couldn't compete against Thomas both times, as for better or worse, people wanted trains they recognise as opposed to awesome, but outside of Japan relatively obscure models, and by the time they got to start selling the Plarail system in the West again, they'd lost the lucrative Thomas license that would have kept the Plarail line selling - Again, make of that what you will, personally I think there was ways they could have improved their marketing, such as making the origins of the trains more clear with a few facts about the model on the box like the Japanese versions (interesting for the kids/adults), maybe selling some of the Japanese steam models as steam trains are universally popular (plus, Hiro in Thomas has given Japanese steam some recognition worldwide), making a few unique 'world' trains like Tomica World had, such as the TGV, Eurostar, Amtrak and HST to add some recognisable stock in with the Japanese (I mean, they could have updated, had an Acela, newer TGV or even a UK Javelin as that was based on the 400 Series so it wouldn't have been too hard to recreate), and perhaps market Tomica as more of an integrated model system that can be both a toy and a long-term hobby (Hint, look at how Hornby et al markets, and push for that).
Same goes for the Tomica cars, because they were never sold in the Hot Wheels single pack format in the UK or Europe I don't think they ever stood a chance against the entrenched Western brands, in spite of being (IMHO) considerably better models in almost all aspects.
It is a shame, as somehow I'm not sure if we'll ever see Plarail again in the West as I think Tomy have been spooked out of a re-release by the popularity of Trackmaster - That said, considering the current direction of Trackmaster one has to wonder wether Tomy may take the opportunity to return again, given that many people preferred (at least, of the people I know) the stuff that was fully compatible across Plarail and G1 Trackmaster track as opposed to the newer stuff that seems only to work with current Trackmaster tracks and nothing else. Honestly though, without the Thomas licence (and let's face it, Mattel aren't likely to give that back to Tomy for the West), I don't see it happening, but hey, these last few years have been so screwy, stranger things have, and could well happen - Should the Plarail revival ever occur, you'd better belive ill be posting pics of a trolley load of goodies from my local Smyths, Toys R Us or whoever has stock, because I'll be there faster than they can say 'Plarail' lol
Been building Plarail worlds since 2001; Building when I can in 2023 
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