Citricsaamreleasing a competitive mode costs them 0 dollars
There's no such thing as a free lunch. The TF2 team clearly sees some potential here and want to explore it. Investing developer time when they could've produced another standard tf2 update says as much. Whether they continue on and invest money into the scene is another question entirely
they also saw potential on pass the time, the mannpower mode, rd_asteroid, and bumper carts etc ..
you know whats gonna happen after the MM update ? 6 months of half cooked updates trying to fix the broken stuff, they will eventually give some things the community wants but most of it we wont get it.
They will throw contracts and hats/skins at it and get revenue of it, but eventually will become stale like every other project they did in the past years.
Do you know why the casual mode was their priority to fix after the competitive update ? Because its the casual community that actually supports $$$ the game, while the competitive community is asking for 250k pool prize majors (pool prize ! not to mention the investment they would actually have to make the organize the whole thing).