There are many gamblers that are vast in sports betting and they bet on different kids of sports games and that's also how often they are devoted in watching, reading and learning about the events and fixtures of those games. Although you are right that making guess on sports that one doesn't have knowledge about could lead to lose of more funds but some player are betting on those sports by using other players prediction.
People who do that are many, however boxing is a sports that isn't supposed to be making a bet without watching the boxers for a long time because is not a sports of how hefty they are looking because you will see a lot of such people taking down easily because they gym to the extent that there muscles becomes heavy for them to constantly throw a punch for a good 30 minutes or hours, so I think is because of how majority doesn't watch boxing that much that's why only few people talk about it betting, however if somebody gives me a boxing game to bet I think I will do it because there is a bit consistency on that sports.