Fluids in the lungs are super bad. They may have a different reasoning, but that's what came to my mind.

I'm no anatomy professor, all I know is dick goes in the food tube, inhaled drugs go in the lung tube and of you do both at once you've got yourself a headlining spot on the circus

It will almost certainly block breathing, yes, but more importantly it's about the opening to the trachea being incredibly small in comparison to the average penis. You can go look at some videos of endotracheal tube insertions and see how tight of a fit those are.

Small edit: looking closely at the picture (which isn't beautifully accurate in the first place, but whatever), the penis isn't even entering the trachea, but the area immediately superior to the glottis. Which makes this slightly less body horror. Here's the wikipedia page with some good imagery. https://en.wikipedia.org/wiki/Rima_glottidis