@DoYaSeeMe because the rabid fanboys who herald TF2 and TF1 as extremely great games that "didn't get the popularity they deserved" don't look at it from an objective standpoint, and don't bother trying to find flaws with the game (of which there are many).
From here: https://www.reddit.com/r/apexlegends/comments/jerb7j/fight_or_fright_event_starts_october_22/g9gmqyl/?context=1000
Developer Daniel Z Klein talks about the main flaw of TF2 and how quickly people pick it up and put it down. It's just innately not something that you can easily sink your teeth into or really get invested in because of how fast everything happens. It's like trying to recount an hour and 30 minute long movie, but only through watching 5 minutes, then skipping ahead 10.
From a personal experience, Daniel hit the nail on the head for me. I picked it up, played it for a week just to get the max rank Scorch paint-job, put it down and never looked back.