You only have to look at some of the responses here to see why things like this are more difficult to implement in the UK. ME ME ME!!! WAHHH IT'S GOING TO CAUSE ME MINOR INCONVENIENCE!!!
I remember when I moved to Munich in 1999 and at that point was used to *no* recycling where I lived in the UK, so it was somewhat of a culture shock going from nothing to recycling and pfand (although as you say the kerbside collections still happen). But once I saw how little rubbish there was compared to the UK and saw the level of recycling that is done I realised it was worth it.
1) You're wildly misrepresenting the objections to this idea. So much so that your claims bear little or no resemblence to the truth. People are objecting to replacing a better system of recycling with a worse system of recycling. Ease of use for people in general is one part of that but only one part and it's not as you describe it.
2) You're comparing a total lack of recycling with this idea. That's a false comparison. The comparison in reality is between this proposed system of recycling and the better system of recycling that already exists in the UK.
3) You blame the higher level of littering and lower level of recycling in UK compared with Germany on the people of the UK but you then blame it on the UK having a better recycling system. Which makes no sense in itself anyway but which also contradicts itself.
The sole possible advantage (amongst many disadvantages) of the proposed system is that it might, just might perhaps, reduce littering in cities a very little bit as a result of homeless people collecting the very small minority of litter than would have a very small deposit on it.
The problem in the UK is not the lack of litter bins and recycling schemes. There are litter bins all over the place and there are convenient and efficient recycling schemes almost everywhere. The problem is that some people are unwilling to use them. Some people will drop litter wherever they happen to be at the time, even if there's a litter bin a metre away from them. That's not hyperbole. It's not even exaggeration. Before lockdown, I used to see it happening daily. There are a lot of litter bins in the centre of the city I live in.
The idea that those people are going to stop littering and/or start recycling simply because a more efficient and convenient recycling scheme is replaced by a less efficient and less convenient recycling scheme is nonsense.