The money laundering laws only require them to investigate large or unusual sums, not to ask lots of questions day to day which are clearly for the purposes of sales.
The banks have found themselves in a situation they can't get out of. 60 years ago, when Captain Mainwaring's type of banking was still the norm, banks took in and paid out masses of cash. Branches processed all the cheques and made the standing orders. Direct debits, cashpoint cards, credit cards and the use of computers were slowly being planned but it wasn't until the late 1960s that they began to change the traditional branch banking.
With computers, cards and the internet the staff of the average branch bank of 60 years ago now have very little to do and the big offices are far too big for them.
The era of selling largely insurance based products was supposed to fill that space. Laws on financial advice were supposed to protect consumers but may have had the opposite effect as independent advice was too costly to provide for a mass market.
The payment protection scandal went on too long and was part of the scrabble for profit to keep the branches going.
Money laundering legislation means banks can now face very big fines if they miss laundered funds. Early attempts to monitor unusual transactions clearly also got used for sales purposes. It's supposed to have stopped. We have recently passed some large legitimate transactions through our accounts recently. No questions have been asked even though large balances have been seen. Both our traditional banks have not reacted to what I'd have expected to be sales prompts only a few years ago.
That's probably why the branches are closing more rapidly. Less selling, little cash to count, no transactions to process, less for staff to do, no need for so many staff, no need for expensive high street branches. Turn out the lights!