This is a fun question, thanks for asking it!
I'm 100% homebrew in setting and adventures, and when I finish a campaign (4+ years for the last three completed) I rarely go back to a setting because I love to come up with new ones. These may or may not have changes, restrictions, and new options based on the setting. I have been repeatedly invited to DM in a shared world that I play in, but for me that's actually harder then staying consistent in vision with settings that are entirely a product of me & what has occured at my table.
I heavily tinker with rules, to the point of making up my own systems (I am currently working on two, one a crunchy combat-oriented that satisfies my Battletech/Star Fleet Battles/D&D 4e/Champions likes, and one a more heavily narrative/gamist where the idea that any one type of scene or challenge consistently takes up so much wall time that everyone needs to be good at it so as not to feel left out is incorrect.
I have several bolt-ones for D&D 5e, and some fairly heavy revisions, such as a drop in replacement for classes. Which I don't play with because the groups I'm with like 5e as is, and some of the players don't really care about system mastery so use outside character builders and such that I don't want to take away from them. (My two house rules are: Inspiration can be a reroll, and bonus action to drink a potion.)