Seems like the UCI decided to make an example of him to try to get sprinters to clean up their act.

https://www.bbc.com/sport/cycling/54899754

Horrible consequences of what he did, but then again the move by Sagan on Wout van Aert in the Tour de France could have caused a nasty crash and he only got relegated in that day’s standings and a CHF 500 fine.

Reading around a bit on this, I think the UCI are trying to combat the idea that the rough-and-tumble in sprints is just part of the sport. Hence the sanctions handed out in the grand tours this year. I know groenewegen has a bit of a reputation for throwing his weight around more than others so perhaps this has been seen as an opportunity to nip his behaviour in the bud a bit.

Still remains to be seen as to what the UCI will do about organisers with crap barriers putting downhill sprints into their races.