Ultimately, still using the Google developed and backed platform gives them more power and control over the market as a whole. If de-googling became mainstream, they would almost certainly fight back, as it undermines the entire business model behind developing these things and giving them away for free.
I know that it's driven in other people's communications modalities.
Whatsapp's success has partly been driven by telecoms companies over-charging.
There is no subsidy, its telecoms companies making a ridiculously high margin (aimed by regulators in some countries) on some services.
My hope is that one day or another whatsapp will enshittify so bad that people will be more prone to move to Signal in the same way that recently Windows got so bad that many users moved to Linux.
Yes, there are certainly banks that block more aggressively, but if you look at e.g. iodéOS's forums most of them work fine: https://community.iode.tech/t/banking-finance-and-insurance-...
Anecdotally, I've also seen a lot of stories of people reaching out to support about overblocking actually seeing success. Apparently there are often enterprise reasons for the block and it literally just needs a customer to complain for engineering to be able to act.
And beyond that, in some countries the strong authentication for logging into government services has been implemented through banks, and so one cannot visit one’s local tax-authority or healthcare portal without a phone that runs the bank app.
One example is my local bus company only selling certain tickets (monthly ones, for example) on the app. If you do not want to use an app you pay per trip which can be a LOT more expensive (several times as much for a daily commute).