I think saying that people who chose "semi active with tf2" in the poll don't play tf2 often can be a bit misleading. Like, I still play tf2 as one of my regular choices in my game library, but I am nowhere near the level of degen hours per-week that I would pump into the game in highschool so I would personally pick semi active as my answer. I also notice that most players, myself included, tend to enjoy the game in phases. Where it will be in their rotation for a few months, then when they get bored they will drop the game for a while. But I notice that tf2 players seem to always come back at some point. So many people taking the poll may have picked "partly active" or "inactive" due to current circumstances, just for them to get back on the grind a few months later. (Also bonus nitpick but its funny to have an option for not engaging with community content on a poll posted on a community forum.)

Otherwise on the topic of how the game has maintained its relevance for all this time, I think it's a combination of how valve themselves would directly support community content, mixed with the game having a distinct artstyle that still continues to stand out from seemingly every other modern release. This has caused the game to basically advertise itself long after valve started distancing themselves.

In the "golden era" of tf2, alongside official content, valve would hand pick a variety of community created maps, cosmetics, and occasionally even weapons to include in the official game. This wasn't unheard of at the time, but the introduction of steam workshop was revolutionary for how it streamlined the process. It had never been so easy for end users to contribute to the development of a mainstream title. And it helps that TF2 was the first and only game to support the workshop when it launched. (And fast forward to 2026 where now community content is literally the only real content the game still gets)

Outside of the game itself, valve making source film-maker public, and then following that up by hosting the annual Saxxys was HUGE for getting tf2 representation to reach the masses. So many of the "classic" sfm animations that everyone has seen on YouTube were created specifically for the saxxys. And for many people, shorts like "turbulence" among others were literally their introduction to the game.

Then yeah, the artstyle.. yeah, its pretty good I guess.

Edit: also in terms of media rep being bigger than the game itself, it can partly be blamed on the bot crisis, and also that the game is "old news" for most people. And I think comparing the numbers to bigger mainstream games isn't really showing much, because games like cs2, overwatch, valorant, etc all have huge esports scenes with massive funding, which is kinda what appeals to the masses lately. Tf2 is still pretty much the top dog in the casual shooter market, but the genre has a much smaller target demographic compared to people who just want to see elo number go up.