Why don't we get male protag games where we turn other men into sissies? This feels like a natural progression of events lmao.
Perhaps, um... because some of us are heterosexual?
Thus we like the opposite sex, dominantly in this case? Also, being a submissive male towards females (or a female dominant towards males) does not mean you have been turned into a "sissy", or you turn someone into a "sissy". Not necessarily. Sissification is its own fetish, not an obligatory part of the femdom genre.
I also hold the controversial claim - and I am sorry if I offend anyone - that sissification is somewhat disrespectful towards females, because if turning a male into a poor facsimile of a female was to be interpreted as humiliating, then implicit in that line of thought there is an assumption, that the female form itself is somehow humiliating, which runs completely counter to my submissive intuition of worshiping the female form. Therefore, turning me into a female would elevate me, not degrade me, so I prefer to stay a male who worships females and don't want them (the females) or their representation used as something shameful.
+ most sissification focused games usually sooner or later makes the hero suck cocks at some point.