There are many states to a flaccid penis.
Every dude on the planet gets severe shrinkage to the point that he practically has no dick. It happens to the biggest boys out there. Just a fact.
There are some dudes who are super floppy when they have a semi. These boys are ideal for porn scenes where "shower" scene is preferred.
Straight and gay porn are both focused on the big boners. But - it is true that straight-identifying men like to see big, low-hanging dicks in pornos. The big, more flaccid-looking cock represents command and respect in locker rooms, when talking a piss, etc. It is the state that is used to brag with your buddies. So, it is fair to say that more flaccid-looking dicks should be shown much more in straight porn because it's what most straight men want to experience vicariously in everyday life.
Just my two cents.