1 person in doors could potentially infect all 50 people in a bar setting, and thats possible in every bar every night its open. It is virtually impossible for one person to do that in an outdoor stadium, even if 25,000 people are in attendance. Not all 25,000 people are going to be sitting next to the other 25,000. The only people at risk are those sitting right next to someone infected for a long period of time, so basically whatever group you're are with. There very well may be some infections that occur that way, but at least it will be easy to contact others in your group to notify them if you may have spread it to them.
25,000 outdoors is more spread than 50 outdoors. These businesses didn't have indoor service