It's not really a "big" pain these days, but it was definitely a problem more annoying than it should have been for much longer than it needed to be. The main problem as you can guess, is that US transfers are either fast and relatively expensive, or free/cheap and takes a few days.
Ofc in this case Musk "solves" this problem as Venmo is one of the most popular solutions, as a spinoff of Paypal. just what we needed, to turn our financial transfers into social media.
Zelle is a much better solution nearly identical to what a bank to bank transfer is, but it's not quite as prevalent.
It's the same with payment system. I hear that bank to bank transfer is still a big pain in the US and that check payment is prevalent there.