Their reward will become tiny in future because 500 invites out of 2,000 is a big deal, but 500 out of 20,000 is rather negligible. Moreover this time with the last validation fail their additional 500 invites will save the day pretty much.
Let's not focus away from the fact that they are collecting rewards for all those invitations. Rewards that are supposed to be spread evenly amongs miners who work really hard to keep their "human status" and look for people who are not going to waste those invitations.
They make the pot of rewards smaller for everyone else by issuing their own invitations.