Payment card transactions can be disputed or reversed. Cryptocurrency transactions cannot be easily reversed. Reversal is an important capability because sometimes customers or merchants lie, or they can have problems fulfilling their obligations.
When the buyer and seller are in the same country, or are in countries with legal and criminal justice systems which cooperate, transaction risk is lower so fees can be lower.
I have an iPhone and a gl.inet gl-e750 portable cell router, and my SIM card stays in the router. I don’t actually restrict my phone the way you’re talking about, but this gives me vpn to my home network without needing the vpn running on each client device. And if I wanted to block connections to big tech company services, I could do that.