Baseball are football are totally different sports. It’s much easier for a Cowboys or Packers fan to visit Vegas, when the games are typically played on Sunday; it’s basically every 4-10 years(sans AFC West teams) so it’s rare, and NFL fans are known to travel.
Sure baseball is played in the summer, but walking on the strip for a 1pm July game is rough(105 degrees); most team’s fan bases aren’t flying across the country to Vegas, baseball is played everyday and not everyone can take 2-3 days off in the work week to visit Vegas.
It’s only 33k seats though so I feel they are factoring all of that in.