I mean, that's how lizards actually are. I can appreciate the "realism" in that design decision, as well as the fact that it gives the lizardman some kind of novelty for developing unique animations. I can also appreciate the fact that the lizardman's hemipenis isn't any more realistic than it already is: real ones tend to be some variety of little barbed bulbs that look like cthulu's nutsack.
Basically, I can understand both sides. Even with mammalian anthropomorphs, many design liberties must be taken to make fucking it not look disgusting, but make it too human and all the fantastical appeal goes out the window. It's a balancing act that will always leave some people feeling like they went too far in the wrong direction.