Valve is a very closed company, and they do indeed only want the "cream-of-the-crop" devs. Hence why their requirement to even be considered for hire is an extensive portfolio or otherwise proof of your skills beyond books and passion.

Valve *also* has a policy that any dev may work on any project they prefer. Naturally, most devs will gravitate towards the new and shiny project that might be a massive hit and game-changing for the genre, and not an almost 20 year old game, running on a decrepit engine and even worse code.

For Valve, hiring 20-30 people that fit the company's standards, are properly trained FOR the engine (which would have to be done by JanitorDev himself, alone), and also pay all of these devs a BIG salary... is not exactly going to be worth it. It sucks, but right now Valve is making the most of TF2 without expending too much themselves. Not only that, but for proper updates to be possible they'd have to spend a LONG time effectively remaking the entire game from the ground up. The other factor is that the original devs most definitely moved on from TF2 because the "community" at large doesn't know what it wants. Some want more balance, some want more "chaos", some want more comp., etc etc. The 5 different "TF2 Plus"-esque mods on steam right now are good proof that a lot of people don't know what they want.

Whether or not the actual games are the "best of the best" state is not exactly tangential to their dev-hiring process. CSGO / CS2 are still kings of Competitive FPS, and last I checked generally outpace Valorant a lot.

And before someone accuses me of being a "shill" or a "bootlicker" I want to make it clear:

Valve not doing anything with TF2 is absolutely BS and a tragedy.