I think it's more of a subsidizing thing. In the UK they get all these things and can't budge due to pushback and culture, so they subsidize those costs with cuts to other places, like shrinkflation in the US, and other places. Costs went up to ship their foodstuffs all over the world, buuuut they enabled tipping at POS in the US, getting poor suckers to make up the difference (they hope)
Not an excuse, but if the US put in place the same things the UK has, fast food would lose their biggest cost subsidy for more expensive places like the UK, and prices would actually go up (because the corpo suits can't take a fuckin pay cut obviously!)
Brexit was in 2020.. Yes, it's been that long.