@TowerOfWashing
If you try and run a store with a skeleton staff because you're making everyone ring up their own shopping to maximise your profits , I would say it's quite clear what will happen.
It's not just "self service" stores though. Places like Greggs have plenty of staff, and don't have self service tills (not the ones I use anyway).
Our tiny privately owned village pie shop/bakery don't have self service and couldn't fit more than two staff (owners) behind the counter. They've had to put the drinks fridge and crisps racks because the counter because of theft.
How many dedicated security staff (because that's what is needed) can shops afford to pay for, just to stand and guard the doors. Even the smallest shop would need two for their own protection and to be useful.
We're really heading for shop counters to be further forward towards the entry/exit doors, bigger and having more stuff behind counters for the staff to get. Like a couple of people upthread have said, we're going backwards because that's how it used to be.
Probably also go back to having tills by the doors (again as they always used to be) rather than at the backs of shops so that customers (and thieves) have to physically go right past the staff before leaving the shop.
It really isn't all about self service tills. In fact if you have self service tills, in theory you have more staff available for the shop floor to watch for shoplifting as a deterrent.