Where have you seen wire transfers processing instantly? It takes 3 days minimum. This is the traditional banking we are speaking about. Who the hell told you it is instant???
There are some countries with systems in place to allow instant transfers. The Single Euro Payments Area (SEPA) are in the process of setting up a European wide payment processor called SEPA Instant Credit Transfer (
https://www.europeanpaymentscouncil.eu/what-we-do/sepa-instant-credit-transfer) which should allow instant transfers between accounts at any time of day or night. Whether or not exchanges will start using this is another matter, but it is certainly possible.
Fiat banking systems are generally pretty slow and archaic, but the US banking system is very poor even by those standards. Perhaps the growth of bitcoin might force them to actually modernize a little.