TF2, according to steam charts, is the third most played game on steam. It’s been overrun by bots for years now, and recently a petition started that’ll be physically printed and delivered to valve HQ. If you care about TF2, or if you can spare some time, please sign the petition
The bots also spew homophobic, racist, bigoted remarks so by signing this petition you stand against the slander!
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It's the same thing with different presentation, I highly doubt Valve is not aware of it, quite the opposite.
It's something that requires a lot of technical prowess to fix (especially to not disappoint the community now). I don't blame Valve employees with not wanting to work with it, especially with TF2 code probably counting as legacy nowadays.
In all fairness, Linux got 64 bit and Vulkan so maybe there's still some people interested but their damage control for bot chat spam (read, disabling chat for free to play) got flamed so that's not confidence inspiring.