I am wondering if part of the problem is that people just take on board exactly as things are - not doing any form of self-safety assessment.
I know of a woman, in her seventies, with such severe respitory problems that she has to carry oxygen with her at all times. She was in a tier 2 area, and went to Bingo two days before Christmas. Then on Christmas day she spent with her son who has Cystic Fibrosis and his wife and 8-month old baby. Now, all of them - that lady, her husband and her son, wife and baby have all tested positive.
She find sit hard to see what she did was wrong, as the Bingo Hall was legally permitted to open and run sessions, then it must have been okay for her to attend. She is now pretty ill, although, fortunately, none of the rest of them are.
I have, throughout, continued to work on my own self-assessment, working well within the rules, but not going OTT. No, I do not wash my shopping ( and have continued throughout to do my own weekly supermarket shop - at a very quiet time), do not isoalate and wash packages and post, etc. But even when cinemas re-opened with strict distancing, decided that was a step too far for me.
As has bdeen said, comprehension of the ever--changing rules does cause many of the problems, and people think if it open then it is okay for everyone.