Why TF would Steam accept something that's not finished?
Can you define "finished"?
In general that's not how art, literature or the gaming industry works ...
The creator decides if his artwork is finished or not ... Steam cannot test and play all the games they sell. The customers have to decide if they want to buy the artwork in current state or not, based on price, reviews, etc
Games on Steam can be Early Access, can be parts of a series, can be a base game + DLCs ...
If you don't like the game and played less than 2 hours, you can refund the game on Steam.