This is a good point.
It's funny, when it comes to legacy financial institutions, I actively don't wasn't their app. I expect that it collected way more information about me than I'd be comfortable with, so I just use their website.
When it comes to self custody, I want to use an open source app (via F-Droid, I don't have Google's Play store).
I've seen too many websites come and go to still believe that sites can't just disappear overnight. Bedides self custody means not having 3rd parties be a single point of failure.