A Salon article from 2011explored why many straight men are attracted to 'chicks with dicks' smut. They noted a series of studies on transsexualism including a paper out of Northwestern University in which researchers recruited 205 men with a sexual interest in trans-females for an online survey and found that 51 percent identified as straight, 41 percent called themselves bisexual and just six men identified as being gay.
Other studies suggest that 'chicks with dicks' porn may be considered by many straight men to be a culturally-safe way to explore their repressed desires to penetrate other males who they are attracted to. Research discovered (by tracking hits to web sites) that trans-porn web sites are usually surfed by guys who also surf straight porn, and they are going to the trans-porn sites not by accident and they repeatedly return. Search engines get lots of hits for "t-girls" and "she males" and these are not usually coming from gay men. Interestingly, there seems to be a high correlation between guys who frequent extreme male sports sites and who play computer war games. As one researcher quoted "[...] for some males there's a very strong need to win, conquer, dominate and show power and strength over other men. It makes sense they'd enjoy being on top of other guys they view as competitors if only there wasn't the negative social stigma of being labeled gay."
In A Billion Wicked Thoughts, Ogas and Gaddam examined people’s Internet porn preferences through data from search engines and porn sites like PornHub. The authors say “if you categorize the sites on the Alexa Adult List by the names of the sites, then T-girl sites are the fourth most popular category of adult Web site.” Also, “‘shemales’ is the sixteenth most popular sexual search on Dogpile, more popular than ‘butts,’ ‘threesomes,’ and ‘interracial sex.’”
It's not an accident that in most of the penetration photos on trans-sex sites, the female-partner's penis and testicles are clearly visible, just inches from the hard cock pushed deep up inside their ass. If they wanted to, the director could easily avoid showing this angle. But being able to view 'her' cock and balls with "his" cock doing her is an added turn-on for the viewer which doesn't require any homophobia guilt or shame because "she" is no longer a "he" in the strictest rules of straight manhood.