GM Manifesto or "What went wrong with my last few campaigns"

I can't believe it's been almost two years since I stopped GMing. It was April 6, 2019 to be exact, and I usually try to be exact. It was a sudden end to the campaign, most of the party had reached 10th level, but it shouldn't have been completely unexpected. Three times before that I had to take a break from the game. Each time I sat down with the players and explained that I felt like the game was becoming player vs. gm, not the characters exploring the world and plotlines that were laid out.
I have only run one adventure path, which was an amazing story. I also did a mini-campaign taking a group through the Temple of Elemental Evil. The way I structure my campaigns is more episodic. There might be an overarching theme or glue (such as: demons and demonic cultists are trying to pull Vaasa into the Abyss), but usually the campaign is knitted together using a collection of modules (often heavily modified) and homemade adventures to fill the gaps. I say that, but in that campaign, I used 2 modules (1 from 3.5E and the other PF1), one mini-dungeon, and wrote the rest of the adventures myself because I couldn't find "just the right" module to use.
Having done this for so many years my general plan is to introduce at least one plot hook, patron, or other source for a "next" adventure in every adventure the characters take part in. It might be a treasure map in the current dungeon, a follow-up dungeon, a clue to a different mystery, or a person who hears about the party and offers them a job. Usually by 5th level, my adventure flowchart (yes, I keep a flowchart) has at least half a dozen hanging threads.
I think the ultimate cause of the campaign's end was the differences in expectations between my players and I. Even after playing with the same group for decades, and being one of the "main" GMs, we just went different ways. About two or three campaigns ago, the focus for the players turned to creating the ultimate character or combat style. Personally, I consider combat the least interesting part of the game (though necessary). Unfortunately, in that last campaign we would spend hours arguing about combat rules, placement on the grid, etc. I tried to move to theater of the mind hoping it would reduce the focus on combat, it just made the players angrier. I had one player switch his character out in the middle of a story arc designed around his original character because it wasn't worth playing the character without grid-based combat.
If the goal of the player is to prove their superiority in developing OP characters, or show off their tactical expertise, then congrats, they've already won the game (whatever that means), cause I'm just not that interested in running that kind of game. I try not to have the game revolve around combat. Certainly, depending on the paths the characters take there can be a good amount of combat, and I do spend a lot of time trying to make combats challenging but not overpowering. If that's all the players want in the game, then everyone is going to be disappointed. Hopefully, I've created a rich enough setting that there are a lot of other things to do.
That doesn't mean taking the party in a completely random direction and complain that it's boring. I will be the first to admit that I don't improv well, and if you go in a completely different direction instead to following one of the many plot hooks the party's been given then there won't be anything prepared. So yeah, maybe it is boring exploring those parts of world that haven't been developed yet, not sorry.
At this point, I can't imagine myself running a game again. However, I felt like I had to get these thoughts down. After all, never say never, and if I did end up running a game again, the thoughts above would be a strong start to a session zero and a discussion of expectations.
I see so much chatter in online GMing and gaming groups these days that the GM should cater solely to the players, but that's not the whole story. Yes, the GM should be molding the campaign around the players, but the players have an equal responsibility to work with the GM. Ultimately, the GM is just another player at the table, although with a different role. If it starts feeling like a "got ya" on either side of the GM screen, put on the brakes and talk it out. If it keeps happening, then there's a larger disconnect between player and GM expectations that needs to be addressed. Everyone's fun at the table is important, and that includes the GM.
I enjoy building worlds, and fleshing out standard campaign worlds. I can spend hours detailing a village, with maps, places, people, and trying to really make it come alive. I won't even tell you how much time I will spend doing the same to a city or large town. I've created and updated (from previous campaigns and systems) many magic items, some of which ended up being way OP (talk about giving yourself a black eye). Even though I stopped GMing almost two years ago, I still create and add content to my worlds on my websites. Never let a good idea go to waste.
With that said, I actually have given thought to what I'd do if I started gaming again. I really enjoyed reading through the Pathfinder 2E rules. Seems like a great ruleset, but it might require too much of an investment of time and energy to convert. The other system that looks interesting is the new Savage Worlds Golarion conversion. The group has always disliked the player class systems and wanted more organically grown characters. I may have to get SW and give it a read-through. We've played Genesys Star Wars. It's a fun system, but interpreting those dice just makes my head hurt.
That means that if I did return to gaming, it would still likely be to D&D 5E. That being the case I am also going through my list of House Rules and editing that list to lean into the game I'd like to run. So expect a House Rules 2021 to pop up on this site soon.
Why do all this? I don't know when or if I'll want to start up again, and I don't want these ideas, including some of the concerns and issues above, to fade away and disappear. To be honest, I'm 55 years old, and I've been gaming since I was a teenager, it's possible that I can't even imagine that I won't return at some point.