the majority of crypto is being held in non custodial wallets, not exchanges.
a better way to frame your comment: why does the world use Stripe and PayPal when you can just go to your bank and ask them to setup a multi day long wire process from bank A to B for less fees?
The 'wire process' is not "multi-day-long", plus a huge number of banks now participate in Zelle, which can be used for instantaneous fund transfers with zero fees. The biggest problem with Zelle is that it looks and feels like a circa-2002 web application.
many wires will be multi days long, encumbered by weekends, holidays, business hours, international checks, and occasional bounces (ask any company their experience with wires for international contractors).
Zelle is between US banks only. some people live outside of the US, surprisingly.
The EU has now mandated fast transfers between banks in the EU.
So, for EU (23 countries) it's not a problem either.
Sending money between banks is both a technical and a regulatory issue (and crypto is discovering why regulations exist at great cost to crypto users). However, "instant money transfer between banks" is not an unsolved issue.
the point is that Stripe achieves some features for certain users that a wire does not. and crypto achieves some features for certain users that Stripe does not.
