No and yes, El Goonish Shive started out as something made when Dan was still in high school (I think, or at least the proto-form of EGS) which started out as wacky hi-jinks, and slowly added transformation elements. People seemed receptive and as such has been running for almost 17 years.
Oddly enough there is only one catgirl (two if you include Felix, who is a dude used for a mostly throwaway joke), but there are many lesbian couples, including, but not limited to: An "anime-style" martial artist with magic, and the genderflipped version of her ex (who can fire gender-changing lasers from her hands); the aforementioned catgirl and a girl who can change the size of things with magic; a pair of griffons from another dimension (one fighter, one mage).
As for why he doesn't draw porn? Because he isn't comfortable making sexually explicit art (provocative is fine and his Patreon is filled with pin-ups and whatnot, just, no nipples or genitals). But he has gone on record saying he is fine with people making porn of his characters and making porn edits of his work.