The longer the penis, the larger the fraction of women who will find sex with that person painful, and at some point the reproductive advantage of scooping out others’ semen will be nullified due to the fact that no woman wants to sleep with you. I think I read that four inches is the length that most women find comfortable, but I don’t remember where I read it.

There’s some thought that this is also the reason for the shape of the human penis

https://journals.sagepub.com/doi/full/10.1177/147470490400200105