Peter P. -
While I understand your post, I think you are missing an important UK constituency that would very much like to see the UK quarantine requirements reduced and/or waived sooner rather, at least for U.S. travelers with proof of vaccination. That is the various British-based airlines (British Air, Virgin Atlantic, Easyjet, Ryanair, etc.) and the sizable UK travel industry (hotels, tour operators, restaurants, car rental companies, B&B owners, etc.). Losing a second summer season of business will leave many of these businesses (and their tens, if not hundreds, of thousands of employees) in dire financial straits.
They have been lobbying the UK government aggressively to find some solution/accommodation.
DT