I don't think you posted in the right forum but I'm gonna tell you anyways.
There are lots of theroies about this but I think the best theory about this.
They made the jungle Inferno update and they expected more players so they tried to do the best for this update like radical changes.
But they f*cked everything up because They didn't listend to old and new TF2 players so they made a bad update in my opinion.
Players left the game because it was not the TF2 what they wanted, crates changed, cosmetics changed, maps changed, servers changed forever. Long story short I think they give a shit about TF2 so in the end they just put some idiotic cosmetics like the banana hat what never fit in TF2.
The only thing what never changed yet is the taunts. (god help please don't change this)
But don't forget google is your friend.You can search up everything

I don't know. however Left 4 Dead is old anyways.