He likes to be dominated and ordered around by the reliable hot guy, he wants to serve his master and wants to be tied in bed. This sub or bottom one finds pleasure in being humiliated, he finds it sexy to be ashamed and actually derives pleasure from a bit of pain. Gay men or gay couples often have this power difference, the other being the dominant or top and the other is the submissive type.
It boosts their egos, this position is for the people or men who want to be in control. One wants to be this party because it makes them feel like a king as if he owns the other person and the latter just lives for the sake of pleasuring him.
He is often the one who imposes what the other does or when should he be pleasured. In bondage porn, there is often a huge and evident difference in the power position, there is the dominant or aggressive party who is the master and would want to be followed by its slave. Through the years, the BDSM community or those who practice bondage porn have popularized the idea of rough sex, the concept of having top and a bottom, sex and slavery and especially the use of different toys to spice up the sex. Bondage porn is popular as ever, you can see popular culture actually profiting off this kind of sexual content.