I have a hard time playing older Pokemon games. It's entirely psychological and strictly to my own detriment, but I've never been able to overcome it.
Pokemon is extremely iterative. Types change, stats change, move sets change, mechanics change, and all these changes accumulate into pretty significant differences. Major alterations to the formula like the physical/special split, or the rebalancing of the type chart, fundamentally alter how different Pokemon function. To me, Pokemon themselves feel almost like software that are continually being updated to create a superior user experience. Playing older versions of Pokemon doesn't just feel outdated to me, it feels incorrect.
I'm playing Red right now because I want a Zapdos in SuMo and I'm having a really difficult time. Not because the tech is dated - that doesn't bother me at all. It's because Gust is a Normal type move instead of Flying. It's because Poison Pokemon are weak to Bug instead of resisting it. There are no held items. No abilities. No Steel, Dark, or Fairy Pokemon. Things are so different that I have to play the game by its original rules and it feels lacking to me. It feels incorrect.
I'll stress again that this is 100% a personal problem. I'm not trying to say there is anything wrong with older Pokemon games. My curse is that any Pokemon that I miss when it's new becomes a game I'll never play. Even now, as much as I love SuMo, I know I will never touch it again as soon as Generation VIII comes out.
I wish I could play Black and White/2. But I just can't. It feels bad to play.