[Kanon]

Exactly. The problem is not that he can't do it anymore, it's that he won't. He's at his happiest when drawing hot girls doing hot things. He's now a popular enough mangaka to do what he likes, and as Kurosu pointed out, this is what he's renowned for now, so he's got no reason to stop.

Here's what Yabuki had to say about Black Cat:

Katsura: It's strange, your previous work, Black Cat, wasn't exactly what you could call a romantic comedy with girls everywhere...
Yabuki: That's true. Back then, I was in the mindset: "Let's make a classic Jump manga!". There were a few girls, but they were not as omnipresent as they are now. My editor, Mister Torishima, egged me on with lines like "We have very high expectations for you", and I wanted to please him, so I followed his direction.

[...]

Yabuki: I am truly grateful for his forthrightness with me. I think that to stray from the laid-out path of (classic/battle) shounen, I first needed a first experience in that field, even if it meant realizing thereafter that it wasn't what I was made for. I debuted weekly publication for a long running series with Black Cat. At the time, simply thinking up the plot of the next chapter took me ages. I didn't have a minute of free time. That period lasted four years, during which it took me everything I had to hold on. When the series ended, I was able to step back to think about what I truly wanted to do.

Katsura: Was it at that time that you considered devoting yourself to your art?

Yabuki: Exactly. That's how To love-ru was born.

Katsura: I understand. We merely have to look at the result to perceive that you truly love what you do, now. I'm under the impression your drawings emit an aura of happiness.

Yabuki: That's true! (laugh). Of course, I devoted a lot of time to Black Cat's art as well, that manga required a lot of work. With TLR, focusing exclusively on drawing enabled me to truly have fun with my work!"

And here are his exact words Obata asked him what motivates (Yabuki asked Obata first to be exact, but he threw the question back at him without answering):

Yabuki: Me, I never tire of drawing cute girls! So if to top if all off I can draw them naked or in suggestive postures, what more can I ask for? (laugh)
However, if no female characters were in my manga, my motivation would drop below zero. That's why women are omnipresent in my works, it's vital for me! (laugh)

Obata: And what if you do get tired of it?

Yabuki: That will never happen! But otherwise, I'd start drawing old people. It's one of my hobby.

I know the last sentence sounds weird like this but it's not (that much); the two of them had previously talked about how old people's faces were interesting to draw, with the wrinkles and all.