Pro Bowl voting is literally a popularity contest and with the season the Raiders are having, fans aren’t rushing to the polls to vote for any of them. And when you put the decision in the hands of the fans, the process is going to be suspect for any position. For offensive linemen, it’s exponentially more suspect.
Few fans pay any a lot of attention to players on other teams who don’t affect their fantasy team. Defensive players at least has some stats to show their worth (even if those stats don’t tell the whole story).