I think specializing in IPA is just the easy way to make something that seems gourmet and exotic, because you can start with a mediocre generic ale recipe and make an interesting lively drink by getting the hops recipe right. And there is so much variety of interesting hop flavors that once you start down that path, there's a lot of directions you can go with it, so there's a lot of room for variety within that genre.
From my limited experience making beer at home, it's much harder to make a mediocre simple brown ale than a mediocre simple IPA. Grain and mashing is harder to iterate on than hops. Apparently the experts make a yeast bread with their desired grain bill as a prototyping shortcut (compared to spending days or weeks brewing and fermenting a batch of ale), but I never got that far before I was diagnosed with celiac and had to give up the homebrewing dream.
From my limited experience making beer at home, it's much harder to make a mediocre simple brown ale than a mediocre simple IPA. Grain and mashing is harder to iterate on than hops. Apparently the experts make a yeast bread with their desired grain bill as a prototyping shortcut (compared to spending days or weeks brewing and fermenting a batch of ale), but I never got that far before I was diagnosed with celiac and had to give up the homebrewing dream.