More importantly, their audience isn't the audience anymore.
After all, it was never a hugely significant number of tinkerers that were important, it was the audience each tinkerer brought with them.
That just isn't the business model anymore.
Could it be that said audience depended on the tinkerers to help with settings things up, but since games "just work" now, the middleman has been cut?
With gaming becoming popular I'd say tinkering gamers are the same number as before, just not the same proportion of the overall gamers pool.
Completely with you on matchmaking. The pathetic limits on these things. You've not lived until you've had a dozen friends all try to climb in/on a drop ship in Tribes 2 in a 64v64 match. That was worth carting a CRT to a lan gaming convention alone. But I don't believe players prefer this, they just don't have a choice. I much prefer the old server-list model.
Messing with computers.
PC gaming today is as simple as going out to Best Buy or Costco, buying a "gaming" desktop, come home, unbox it, plug everything in, initialize (note: not install) Windows, install Steam, and Bob's your uncle.
Most of us hailing from the 20th century learned how computers worked because we kind of had to to run the games we wanted to play. Memory address allocations, DLL hell, driver hell, registry tricks, picking out parts and putting it all together; all stuff gamers today simply don't have to deal with. Windows Update will even figure out most if not all the drivers for you.
And before anyone says it: Yes yes, I know buying a "gaming" desktop from Best Buy or Costco isn't ideal. But guess what? We are outdated oldtimers. We definitely know how to get the best stuff, but gamers simply don't need the best anymore. Computers have become household appliances, not tinkerers' toys to be handled by wizards. So what if that desktop from Best Buy craps out? They just go and buy another one like you would buy another Playstation and Bob's your uncle.
Gamers aren't tinkerers anymore, most people don't mess with computers anymore.
My experience ~30 years ago involves a 386, big-box computer, Window 3.1 pre-installed. My options for tinkering (outside the battle for HIMEM) were pressing a turbo button and hex-editing File Manager to File Mangler. There was no hardware modding scene at that level, just a choice of massively expensive storage and RAM. I'm sure there was more that you could describe as maintenance but I don't consider myself any less of a hacker because I don't have to run "hdsit" before I shut down.
Did I do more stuff? Sure. I didn't have a huge number of games so writing your own, playing with tools was pretty much your only option, and I would agree with a characterisation that people fiddle with computers less because they have less contact time with an actual desktop environment outside of the browser. We are spoilt for choice.
But PC gamers still tinker. The have hardware options unimaginable in the 90s and the scale of game modding scenes for things like The Witcher 3, GTA5, Fallout 4, Skyrim, Minecraft, Souls and Rimworld eclipse those efforts in the 90s, many times over. Shader beautifiers weren't even possible. Is it niche? Probably, but PC gaming has always been niche.
Gamers aren't tinkerers anymore.
Times change, gamers might have been tinkerers and hobbyists who accepted needing to mess with their software and perhaps even hardware (memory address allocations, anyone?!), but that was 30 to 40 years ago. We're in the 21st century now, more than 1/5th of the way to the 22nd, and gaming has become mainstream.
Gamers today just want to play games, messing with the computer (what's a computer?) is above their pay grade. Games today route multiplayer through their own matchmaking servers because Player-2-Player matchmaking /fucking sucks/, it's janky under ideal circumstances let alone normal. Gamers today don't want to deal with network shenanigans, they just want to play; so devs and publishers oblige by handling more things on their end simplifying the experience.
Gamers aren't tinkerers anymore.
The gamers of 30 to 40 years ago have moved on to messing with "home labs" and Raspberry Pis and 3D printing and shitposting on HN.