Below are some reasons I remember reading about:

In the uncircumcised, the foreskin must be retracted and cleaned all the time. Back in the day, a lot of little and big boys wouldn't do it often enough - or properly - leading to crusty infections and smelly members.

Also, sometimes when entering puberty, the foreskin wouldn't retract fully when the person had an erection, causing pain and twisting.

And according to some, an uncircumcised penis is much more sensitive and would have a much shorter 'release' time, leaving the females unsatisfied with the quickness of the delivery.

Years ago, I knew only one fellow who was uncircumcised as a baby (everyone else was, as was their brothers and fathers before them) and hated his uncircumcised look so much that when he was in his early 20's and could afford it himself, went in and got it done. He said the ladies had reacted negatively to his intact look and that it was so sensitive that he had no endurance before release, so that was a problem, also.

He said once he had the surgery, he was much happier and had neither of those problems post-surgery.