I wondered, for the longest time, how this situation came about, but I heard a podcast by a train expert and he pointed out the economic incentives the government idiotically gave Deutsche Bahn:

If they have to replace something with a new version, then the government foots the bill, as that's a New Purchase and an "improvement" and "environmentalism".

If they have to repair or care for something in the maintenance phase, then that is "upkeep" and they are stuck with the bill.

So, they just let everything rot until it was irrepparably damaged, and then had it replaced. So, stuff had to break, before it got fixed. So stuff broke, and broke, and broke...

Throw-away fashion and Vibe-coding, but make it trains.