According to results of the Second AB/DL survey, the AB/DL community is about 12% homosexual, and 6% homosexual-leaning bi.
True. Another factor is that heterosexuals might be more likely to have families, and less likely to have much time to spend online. Some furry forums, such as furrymuck or secondlife, can take up much more time than some AB/DL forums, such as dailydiapers.
And according to the survey 84% are male. Combining the Homosexual, Bisexual, and Leaning towards Homosexual categories that creates a total of ~30% of men considering sex with the same gender. And with regards to the total population, there are more male ABDLs interested in the same sex than there are actual female ABDLs in total.
This is why so many gay male DL sites exist, and why no (to my knowledge) lesbian DL community sites exist.