Well, I also see a fair number of servers, with real players, but not even I hold on to that and I don't consider that a stable player base to play with, and the number of players is getting smaller, not bigger.
The most popular gametypes are stuff like Siege, IG, pretty much anything to do with either CTF or DM.
MH is still fairly popular, but not as popular as those, and it splits mostly between NW3 and non-NW3 servers (there was a DM server before with NW3, for example, which was fairly popular maybe 2 years ago, but it disappeared).
Having that said, if the game was ever released by Epic for free (not only UT99, but maybe all of them), I would wager that we would see a lot of incoming players.
First a brief record-setting peak in years, to a quick decline, but stabilizing at a number of players (and potential mappers/modders) far higher than now.
Also consider that UT99 is now an "old people" game, as in most of us are probably already 30 years old or older, there isn't exactly much young blood around playing this game as far as I know, and all young people are getting into more modern games (like the infamous Fortnite, for example), meaning that the game will likely definitely die when we all leave it for good at some point.
Having that said, I always wanted to personally do a few things to improve the game experience and attract people to it, be it new players, or returning players.
One of them was already pretty much done by Shrimp, with the UnrealArchive, which was built almost exactly how I imagined that type of repository to look like, with all the automation, metadata, multiple mirrors, great presentation, dependencies lists, search mechanism, color schemes, and so on and so forth.
The others I had the intention to do were stuff like an universal manager to deal with everything about the game (manage mods, maps, game patches, easily, no more umods or knowing where to copy stuff, or what to delete to uninstall), in-game news and events about the community and the game overall, editor plugins to search, share and download resources with the rest of the community, as well add more useful tools, save and retrieve common configuration profiles, maybe even an automated (small) pool of servers people could matchmake in and play with whichever mod configuration they wanted (maybe to the point to click in a "quick play" in UT and just enter a server), etc, etc (you can imagine).
And in a way I haven't exactly completely give up on that front, it keeps popping up in my mind, and I have been developing something that would help me get there for the past few years (as well be useful in RL, which it has been, greatly so already), but I am still very far away to be able to actually do something about it, be it in terms of resources, time or even motivation at times, because I also see things in the community that leads me to think "why bother", which is something I believe constantly crosses everyone's mind, but immediately after you just run the game, play it, and you do then remember why.
Sure, the game is not as popular as when it launched 20+ years ago, and you will find the same people most of the time, but yes, you can have your online fun. So why do people say the online is dead? Don't expect Fortnite volume, but if you want to play online, you sure can. Or not? 
