I’m not sure why other banks haven’t followed. One month treasury rate is already up to 2.3% now and banks can certainly lend it out at higher than treasury rate.
But credit unions and especially new small players like Robinhood aren't going to threaten PNC or BoA or Chase. So why would they give up free money if they don't have to?
Remember we're talking about checking accounts, not mutual funds. It's not a real investment. You might as well get something even if it's small.
Basically, Robinhood is subsidizing this 3% interest rate with investor dollars. Of course, there having a higher reserve lets banks lend out more money, but I'm not sure that's worth paying a 1% premium over.