One thing that has happened is that I've liked seeing the merge
message things that have come in through signed tags so much that I've
decided to try to write more explanations even for the merges that
don't get that kind of love from their subsystem maintainers. Some
subsystem maintainers (David with networking is a good example) have
tended to write nice good explanations in their pull requests, and
I've started to try to make those kinds of things part of my merge
messages.
I'm not sure how many people really look at merges, and maybe it's a
waste of my time, but I thought I'd try it. I've also spent more
effort trying to explain even fairly trivial merge conflicts (although
the truly trivial "touched next to each other" that just aren't
interesting from a code standpoint I generally have left without
explanation).