I don't think it's been ignored. Birth control pills for men would be a massive money maker. (Here is a recent article I found on BC for men: https://www.nih.gov/news-events/nih-research-matters/male-contraceptive-disables-sperm)

While I am speaking way outside my confort zone here, it seems magnitudes harder to effectively disable millions of sperm and their associated production as opposed to simply knocking a woman's hormone balance a little out of whack to prevent ovulation.

The bigger question is being ignored though: If we have to inject our scrotum with a gel, where are we going to store our pee?????

Unfortunately there has to be almost no side effects for almost all users, as there are no (as yet) medical benefits to male contraception.

In women, not being pregnant can prevent death for some of them, regulate painful periods, etc. - it is considered the risk of the myriad side effects is worth it because at least it does some good.

For men, who do not become pregnant, not being able to get someone else pregnant is not a medical benefit for the man.

And unfortunately hormonal modification does cause problems. Lots of them.