It may because vote trading and vote selling (which are equivalent) is damaging to the game theory behind PoB as has been explained in posts many, many times going back three years.

So it comes down to value. If someone is doing damage to PoB then they may not be contributing on net, even if their posts are otherwise okay, and rewards should follow value contribution, or they are a waste of money.

That, I guess, is the logic behind curangel and others prioritizing these downvotes, but that is up to them as with any stakeholder deciding how to use their votes.