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?????