My first reaction was towards this sentence from your opening post: "Seriously, out of the how many thousands of players?" That's where I think you were overestimating. I think the number of players is not that high anymore today. Which leads to only 1 server, if lucky 2, being populated and thus ending up with the same players match after match.
Even if there's thousands of players, these are spread out between several regions, and on top of that 5 different platforms, and then there's crossplay on/off to make a further segregation. Add to that the different featured game modes (I counted 10 this week alone, not even taking non-featured portal modes into account), and it's becoming easy to spread thin thousands of players.
I see the same thing happening here. If I go on CQ64 I mainly encounter the familiar names. The weekly event game modes tend to be more populated with new players, but these are not the type of players that stick with the game for long. Especially if these new players venture out to CQ64 and are being confronted with those high level frequent players.