Banks in the USA do not allow deposits into accounts without account holder permission. They won't let you stop by a branch and deposit into a friend's account (to pay them back) without a formal arrangement, so it's easier just to find your unsophisticated friend and give them cash directly. I'm not sure if this is due to a law, or our culture of security theater.
This is not (universally) true. I've had many friends/family deposit checks for me at my local branch when I'm out of town/on vacation/whatever. I've done it myself for other people. I believe the banks in question were Wells Fargo and US Bank.
YMMV based on bank, but there is no regulation preventing this.
The reasoning presented was a little suspicious - they envisioned someone "forcing" you to unwillingly take a loan (of like $100) by depositing it into your account. Then they would demand their $100 back and use this as leverage to blackmail or otherwise disrupt your life.
But I don't totally disagree. To me, depositing money into another person's bank feels...improper - like performing an oil change on someone else's car, or taking someone else's books back to the library, or walking into your neighbor's unlocked house to lock all the doors. There are very good reasons someone would want these done for them, and also edge cases where these would cause an issue for the other person. It's a moral grey area to me.
Definitely not the case in many (most?) banks. I've done this multiple times and never been turned down.
My first hand experience (2017) is that US banking oferring (from a european guy perspective) is a eyes opening experience.
* There is no instant bank wires (free ones) between major banks. Or at least the same days ones, working reliably through most of banks.
* You get paper checks from your bank :)))))
* Small business (sold a car, got a return from landlord) give you money on checks, also accept only paper checks if you need to pay them on the spot (in the office).
* your bank charges you a monthly fee, to protect you from overdraft (wtf is this on debit account??), he shall block from happening at the begining - we call it "protection racket" in Italy.
* boa/citi and others have websites with design from 2005, not to mention mobile apps..
* you can't send money from bank account to a different bank to your unsophisticated friend (plumber, maid, or mr sandwich) just knowing his phone.
* when you withdraw money from coinbase to your connected US bank account, you pay 1,5% of face value. WHAT? PERCENTAGE FEE? This is USA banking thing, as the very same coinbase, charges fixed 0.15 EUR fee per no matter how big wire if you're european.
* major us banks got two factor just two years ago in terms of security.
* tap to pay (we call it paypass) is also almost 10 years after europe.
* first chip card in citi was offered to me in 2015 or 2016? Still magnetic (easily copied) card is used in majority of points in the USA
etc..
Some of them are chaning in the last two years, but mostly for sophisticated customers, small banks, and people not being able to use those features between different banks. It will still take a lot of time to catch up with a Kenya from Africa...