Playing sissification game to resist whole transformation is kinda counterintuitive, in most games it would just get you punished and force on you feminization anyway, otherwise if you'd be able to resist completely wouldn't it just turn into vanilla game? Other than that option to resist sometimes used to skip some content that is hinted to you, but you know you won't enjoy.
Ofc more choices wouldn't hurt, but authors that develop sisiffication games don't want to bother with vanilla routes, and players mostly don't need it, cause they can find tons of vanilla routes somewhere else.