Pretending PG didn't already respond, I'd say that you won't find many VCs investing in porn at all, because it's not really a business that scales well.
as for investing... most of the good ones have the cashflow to fund their own growth. online ones (lightspeed media, rki) and offline ones both have grown insanely over the years.
I'm not sure why you've been mercilessly downmodded, because in a roundabout way you are correct.
The obvious answer is that porn has an associated stigma attached to it that makes it a rather unattractive business venture to get involved in. If you are prepared/don't care about being painted with that brush, you get into porn production.
If you do care, or people you respect care, you avoid it.
