Plarail μSky 20th Anniversary

Here's my personal theory: I think the μSky hits essentially a sweet spot, being both iconic enough/a good enough seller to continue production, while also not being replaced in real life with another type of rolling stock. Let's take for example the JR Yamanote Line in Tokyo, arguably one of the most iconic non-Shinkansen routes in Japan. Since 2002, Plarail has been continuously producing official Yamanote Line trains under designation S-32. Before that, going all the way back to the 1970s, Plarail had been continuously manufacturing green JNR commuter stock that mirrored what ran on the Yamanote Line at that point without being officially designated on their packaging as Yamanote Line trains.

However, the Yamanote Line is a very important route for JR East, and as such the real rolling stock gets replaced with new sets pretty frequently, To keep their lineup accurate, Plarail also releases new trains replacing the former ones. This happened in 2002 when the S-32 green 205 Series was replaced by the S-32 E231-500, and again in 2020 when the S-32 E235 was introduced, which is still made to this day. So even though Plarail has made Yamanote Line trains for longer than the μSky, since they've had to produce different types of trains to match the real line no one single train has been made for longer.