I think the service charge was introduced because of people not tipping. Tips have always been understood by most people to be an important part of waiting staff's pay
i think it’s more likely so restaurants have control of tips, either so they can dish them out fairly, adhere to HMRC rules of tax/NI, or in worst case take a % before staff get it. I have worked in places where the service charge is not passed on to staff, or is distributed by seniority, so maitre d’ and head chef get a bigger share, junior wait staff barely anything.
i also wonder if it can be used to monitor staff performance, if you aren’t collecting enough tips, pressure applied, so even if staff are better off with cash, they refuse.
service charge is discretionary anyway, so people who don’t want to tip will ask for it to be removed. Fairly sure in a lot of places you are asked by the card machine yes/no and what %, so you don’t even have to ask.
if I’m somewhere that automatically applies service charge, I will ask the wait staff whether they’d prefer cash or it added to the card.
and yes, completely agree with pp who says they avoid places where it’s clear staff are behaving with one eye on tips, upselling etc.