There's been plenty of discourse surrounding this topic and most conclude selfishness, but I doubt this is the whole picture. I've noticed a difference between descriptions of sex between cut men, intact men, and intact women. The cut men often describe sex as a race to finishing while both intact men and women describe the experience with more sensual detail. I believe cut men experience less pleasure but don't realize it and engage in sex more too aggressively and fast, leading to a quick orgasm for the guy and an unpleasant experience for the (intact) woman.

My Reasoning for Circumcision decreasing sexual pleasure:
It's irrefutable that FGM victims struggle with sexual dysfunction. We also know that every person's genitals are the same structures which develop differently based on hormonal exposure. If the structures are analogous and we know how removing these parts hinders a woman's understanding and relationship with sex, it follows that similar sexual dysfunction would occur to any GM victim regardless of gender. We can also expect pleasure to be reduced since the parts removed in a male circumcision are the most erogenous parts.

I'm certain there are plenty of genuinely selfish dudes, but a lack of understanding is usually more likely than malice. Cut men would understand sex better if they still had their most sensitive tissues.

EDIT: Improved the structure of the claim