season 2 isn't being reduced. the original order was for 18 episodes, then they expanded it to 22 around Dec so they filmed 4 more episodes but they are sort of a single arc not tied to the main story. The 18th episode, aka original season finale, is apparently super dope and ends the season well so they would rather finish it that way and tack these extra 4 episodes onto next season rather than end strong and then continue another mini arc.
It was all a decision by the show runners and Fox respected them enough to allow it instead of forcing them to air the 4 episodes. I think its all a good thing. Also I'm not sure if season 3 will be 26 episodes or they will just air 22 and have 4 already in the can, I read its the latter.