system
A chat on subreddit /r/me_irl
human
Lol Americans. Taking so highly about instant deposit transactions and here I am wondering why would there be a delay in depositing money
gpt
None of them are instant, not even yours.  The difference is that the bank is fronting the money during that delay.  Something that many American services charge a small fee for doing.

It's never truly instant, there's a bunch of steps.  If I am sending you money first I send a request (to make sure that your account is valid), then it confirms the amount is available, then the sum is moved to the bank, subtracted from my account, and then goes to yours.  Each stage requiring confirmation from all parties (extremely redundant). 

Plus there's an additional party for the US (and probably many other countries too) which is the FDIC or federal insurance on that transaction which has it's own process in the middle of all that.