If it wasn't for the fact that I bought a car for about £1400 in fifties in about 1996, I have spent more $100 bills than £50 notes in my life. I have only visited the US on a few occasions for holidays.
£20s are more than enough for most things. They are not too big or thick so even £1000 is just about manageable in a wallet for a short time. Larger than say £200 at most is bank transfer stuff. We have had near instant bank transfers for years. To be honest I keep a cash float of about £100 but I am an older bloke and like to use cash sometimes. I could easily operate cashless for about 99.5% of the time. The number of transactions that I can't do with pay by bonk (NFC) or mobile banking is absolutely minimal. I only use cash in a pub out of habit to be honest.
I've gotten them before when pulling out a few hundred dollars, but since most ATMs have a limit between $400-800, I guess it makes more sense to just stock them with small bills. I've gotten them before, but if I need more than $100 or so, I'll go into the branch so I can get exactly the denominations I want (e.g. I wanted $100s when I bought my car or for gifts, but I want $1s, $5s, and $10s for baby sitters and tips).
From what I’ve heard, £50 notes are used more rarely than $100 bills are here in the US.