Why are Plarail Ashima and Yong Bao so expensive?

[SORRY, I accidentally posted this on the Trackmaster and not the Plarail forum. Mod, if you can please move to the correct area?  Thank you!]

As I am adding my plarail to spreadsheets, noticed I don't have TS-18 Yong Bao and TS-23 Ashima.  I know on Amazon JP back in 2022-2023, I was waiting for them to come back in stock as they were sold out but if they did, it was a third party who wanted a lot for them.

But now on eBay, they are expensive.  

I know they been out since 2018/2019, but at least with the other in the TS-line They often get replenished and sold on Amazon JP except these two.  Even when I traveled to Japan, I couldn't find these two at shops.

Is there a reason why these two jumped in price and became so hard to get affordably.  Were they out for a short time?  Don't understand why these two, Amazon JP never got anymore added to the store compared to the others in the TS-line.

They got discontinued i believe ashima did this year so the price will go up.

There's no way they are expensive, they are only 6~ year old models, it can't be!

But of the 24 last releases which are as old or older, why these two?

Very strange, Ashima and Yong Bao aren't that popular characters and the models itselfs aren't that good too. There's something behind closed doors or people thinking if a product is discontinued equals rare and hard to find.

Had to pick up Ashima sooner than later after her discontinuation because she was already pretty expensive prior. Absolutely no idea why.

Yong Bao I've got nothing on he's an enigma to me