This is why it's worse than ever. People aren't even being as careful as they were in April/May. I'm not sure I understand why it's so hard to be prudent for more than 5 minutes.
We're a social species. We have family. We have friends. Going 6-7 or more months without having that contact is emotionally difficult. And while Zoom calls and texts/phone is one thing, they're not really a substitute for actual human contact.
All the simple stuff about physical distancing, wearing your masks, etc when out in public is EASY. Nobody IMHO is really all that worried about mask fatigue. It's not hard, just annoying.
But that lack of seeing family and friends is something people are having trouble with, and so they're starting to do that. And as has been pointed out, a lot of the spread is from small gatherings, from family/friends rather than "the public". And for many, there are things like weddings, births, funerals, major birthdays, etc, and people won't [or can't] put those major life events on hold forever, so people consider it important enough to attend despite the risk.
I doubt these gatherings were all that big of a deal during the summer BBQ holiday season, because I'm sure a lot of those gatherings were outside, in the sunlight. Coming up here in a few weeks is going to be the big one, and late December there will be another, because there will be large family get-togethers in cold climates and inside.
People are willing to wear their mask to the grocery store to buy the turkey, but they're not willing to not see their family to celebrate Thanksgiving.