I'm not so sure about in the games whether there's more than 8 Badges. While it could be player perspective, in the games world if feels like being a Pokemon trainer is more restrictive, not many trainers have many Pokemon that almost only the Champion has 6 Pokemon (yes there have been other trainers with a full party, but they are very few and far between... and one of them is a joke with 6 Magikarp (sometimes 5 with a Gyarados thrown in for lulz)). To many trainers the Gyms are very difficult to beat, the Gym trainers are probably on their level and the Gym Leader is quite above. Meanwhile the player and their rivals are pretty prodigies, they somehow have the gift of being able to balance out training a full party of Pokemon and ready to defeat the Gym Leaders usually as soon as they get to town if not before. Like one example I remember is that in BW there's this Roughneck in Striaton City who says he's having a difficult time beating Cilan, Chili, and Cress. Two years later in BW2 we meet the same Roughneck again who reveals he never was able to get the Trio Badge and now the Striaton Trio are no longer Gym Leaders meaning he'll never get it. Is that Roughneck really that bad of a trainer? Or is to a normal NPC maintaining a team of strong but even leveled Pokemon very difficult due to real world restraints they but not the player experience. If so the game world doesn't need more than 8 Gym Leaders as they probably sweep through unprepared challengers and those challengers don't challenge again until after a lot of training. It's probably also why we go straight to the Elite Four after getting our Badges, all those trainers in Victory Road may have 8 Badges but they're not prepared to take on the Elite Four and especially the Champion.
Meanwhile in the game world I'd say Pokemon training is a much more spread out thing. There's more trainers which mean there's probably plenty of trainers who have potential, way more than we see in the games. Thus there can't be 8 Gyms because otherwise they'll be overwhelmed by challenges. Also it seems like to becoming a Gym Leader is different in the anime than in the games. In the games it feels like those who became Gym Leaders were scouted out, like the Pokemon League is always on the watch for trainers with potential (and probably a preference for a certain type). But in the anime with so many Gyms it probably runs like a franchise where you call up the the Pokemon League, say you want to become a Gym Leader, and after testing you if you pass you get certified as a Gym Leader. So we not only have more trainers trying to compete in the Pokemon League but also more skilled trainers asking to become Gym Leaders. Finally the increase in trainers in emphasized in the anime's Pokemon League which is a tournament of trainers with the winner getting the chance to face the Elite Four and after them the Champion. And you don't get to try and try again, if you lose you have to start all over so the anime REALLY weeds out trainers.