I'm currently working on two fantasy books and an erotica book. For a long time (like 4 years) I focused exclusively on fantasy, but it can be fun to switch things up with another genre occasionally.
I carefully considered whether I could write quickly enough to sustain two pen names before I started taking the erotic work seriously, though. Unless you're one of the lucky few who becomes a bestseller quickly, making a living at writing means building a readership in the genre, and any works that don't match the genre aren't going to help with that. Lots of writers have been successful across multiple genres, but you can't write everything. Plus you have to have read hundreds of books in the genre to have a proper feel for it, as well as keeping up with ever-changing market and reader expectations for each genre you write in. Two is more than enough for me.