Just like with a lot of things. Sure you could do a thing better, faster, more efficiently on a PC, but some people just don't care when 80% is good enough.
My boomer dad does more things on his phone than I do and I'm Gen X. It's actually astonishing how much he does on his iPhone. I'm dragging out the laptop and he's on his iPhone happy as a clam.
I've heard that GenX/Millenials are in a sort of PC goldilocks zone. People older than that cohort don't know computers and therefore use phones for everything, people younger don't know computers and also use phones for everything.
I'm a tech loving boomer, I always use my PC for banking, ordering, etc. My wife, however, almost always uses her cell, which is great for when we are traveling. Even though we're only five years apart in age, she's lite years ahead of me with a cell. I freely admit part of my reluctance for using my cell is the mobile tracking ability of companies.
I used to be with ‘it’, but then they changed what ‘it’ was. Now what I’m with isn’t ‘it’ anymore and what’s ‘it’ seems weird and scary. It’ll happen to you!
that's kind of an ad hominem, but also beside the point: most bank apps (and websites) are actually absolute garbage, especially the top ones, just one example: the Citi app (on different phones) for a very long time refused to allow me to make a payment or change my password, so i had no choice but to use desktop. Somehow still, top banks' ugly websites seem to allow more functionality/fewer bugs than their mobile apps, which are very often just dumbed-down webviews or simplifications of their websites.