Roster question

I see a couple teams waiving and adding new players this week. Obviously the fever down players needs to add someone temporarily. But the other two being from the sun & dream. Im a newer fan so I didnt know you could do that mid season. To my knowledge those additions are because those players aren’t adding anything to their teams and they want to try something else. But why are they allowed to do that? Like yes they may suck but you selected them a couple weeks ago?? Shouldnt they be required to try and work with them for the season?? Please correct me if ive got it all wrong lol.