Oh but it's not the new ones that is a problem (why wouldn't they put them on everything to begin with?), but the old games.
It's one giant story to follow, and good luck putting your hands on the first 3 games if you're a console player. You play on Switch, what do you do? Well, not much, and that's the problem
It's even more stupid if you're on Playstation, where the first two games were released multiple times. But you can't play them on your PS5. And the third game didn't receive a western release on PS platforms anyway.
When there's talks of backward compatibility, it goes beyond playing that one game you liked 20 years ago.
Trails is definitely the best example of that.