Right, but since it is open to the public anybody could vote, not just GM's. I dont see the big deal
Again, remove voting of your own team out of the process and that gets rid of the perceived bias of two GMs guaranteeing two first place votes even if everyone in the league can look at the teams and know that they don't have the best teams.
This year Portland and Orlando had two of the better teams in the league so there's no big deal that each team had a GM and AGM voting them #1. But, for the sake of argument let's chose two teams from this year that barely got a vote higher than 10, Miami and Charlotte. It's pretty obvious to all that those were not teams that would win their conferences. But if they each had two GMs and they both decided, even though they knew their team couldn't win the conference and they voted themselves #1 in the conference, that's 4 votes that are really moving placings around and could effect a vote that has only a total of 25-30 votes.
In this year's draft, it didn't matter because of the quality of the teams managed by two GMs but in the future it could be a scenario of contention.