The Kongversation 1227 - Sea of Thieves: Season Twelve 

K. Rool does deploy a few more Kremlings bosses later on (in games like Jungle Climber), but it seems K. Rool just prefers large bosses, and for whatever reason, it's the native non-Kremling species of Crocodile Isle that are more likely to come in deluxe proportions. Therefore, the Kremlings work better as grunts in the field. However, there are a few enormous Krems, and K. Rool did put them to work: Kerozene in the GBA remake of DKC2, as well as K. Lumsy. Seeing as how the latter immediately abandoned his post when he refused to commence the attack on DK Island, K. Rool probably feels secure in mostly sticking to enormous Gnawties and Zingers. The real-world answer, of course, was that it was easier for the original DKC team to blow up the smaller baddies, and that sort of set the template for everything that followed.