Head coaches and GM's would show favoritism. The AP I guess chooses which sportswriters they think are experts who follow the league closely and objectively evaluate who deserves all pro nods and awards like MVP. It's a way better voting session that the pro bowl which is a popularity contest (players, fans, coaches all vote). For example, Kirby Joseph was voted first team all pro which he deserved but wasn't selected to the Pro Bowl. I don't know if there's a better system as it's far from perfect just looking at some of the television personalities or former players who get a vote.