Same Day ACH has been in the works for a while; however, a payments expert I spoke with said all the big banks are opposing it since (a) they make more on wires, as mentioned, and (b) most of them have in-house same day transfers, so it's an argument for opening multiple accounts with them vs at different institutions.

https://www.nacha.org/content/same-day-ach

The electronic financial system in the US is an embarrassment, to be honest. Instant transfers have existed in other countries for years. The only platforms that allow instant payments require (a) holding money in their bank account (e.g. your Venmo balance) and (b) the companies to comply with incredibly stringent money transmitter laws.

From what I've heard, Stripe doesn't make much from CC transactions (hence why almost all providers are at the same pricing). ACH costs fractions of a penny, so even if they only make $5 it's nearly 100% profit.

[Note: I'm not a payments expert so would love if someone who is could (in)validate all the above.]