It's the result of weird ethical standards, which make the side effects justifiable for women since women experience all sorts of effects from periods that can in some cases get better with hormonal birth control. The fact that someone (many people I'm sure) might choose to deal with these side effects in exchange for their partner not having to, or just for additional safety, doesn't factor in there.

I honestly think it's rooted in the same beliefs that also make it hard to get any permanent body alterations done if not deemed "medically necessary". Things like a vasectomy or HRT, both of which reportedly have tons of hoops to jump through to get them.

A lack of trust in people to be able to decide what to do with their own bodies.