While this sounds like a good idea, in the modern landscape of PvP games, it would never work.
Current player expectations for PvP games are now “click play, get into game”. Every layer of friction filters out players who don’t want to go through the hassle of being able to just play the game they bought.
It seems easy for you because you played multiplayer games in the 90s, but anyone born after that era will have to learn to filter through a megalist of servers with names like “BoB’s L33t S3rv3r”.
But let’s play devil’s advocate and say the devs could still add the self-hosted servers to their game in a couple different ways.
If devs added it to accompany the default matchmaking, there’s now the problem of their player base being siphoned away from the main matchmaking pool, which further destroys the default player experience.
If devs added self-hosted servers as a way to supplement their own matchmaking servers (e.g. officially hosted servers + player hosted servers), the player experience can now wildly vary depending on which server you connect to, especially since devs can’t guarantee the same experience on random Joe’s home ISP connection and server hardware.
There’s no winning for the devs. While your sentiment is valid, the practicality of doing it is not feasible anymore.
The sunsetting idea is good though and I wished that happened more too.
I have no idea how any game client and server implementations work (outside of games I’ve actually worked on), and I’m pretty certain you don’t either, so saying something is “zero effort to add” is presumptuous and naive.
None of what you’ve said solves any of the issues that I pointed out, only “look at how much extra gameplay you might get!”, and that’s assuming the devs took the time to make their game easily moddable.
For a primarily PvP game, the biggest challenge a studio (especially a small or mid-sized one) faces is gaining a large enough population of players early on. Without critical mass, the player base will rapidly dwindle because people get tired of waiting in queues for their games to start (whether it’s by matchmaking or finding a custom server), or the quality of the games get worse because they’re constantly getting matched outside their skill level (stomping or being stomped).
Providing examples of games from Valve doesn’t prove anything because Valve is an extreme outlier. They can afford to put a game out with zero marketing on their part and achieve 170k player concurrency - what other studio has that?
I’m not disputing the potential advantages that you’ve brought up - I’m only trying to explain the rationale that devs without virtually infinite time, effort and money have to contend with when working on a PvP game.