I think there’s three reasons it hasn’t been a priority
1) You’d need to have an advantage over condoms, which are super cheap and extremely effective. You could argue convenience, but if you can’t remember to have a condom around, are you going to remember a pill?
2) Because there’s no cycle to work with, it would have to be a constant change to your hormones which is probably pretty tough to predict the long term effects of. Guys don’t have a natural “off” state you can mimic. So there’s a higher ‘scary’ quotient and might add some resistance to people starting up with it.
3) No protection against STDs, which gives an advantage to condoms
Like omfg said, it’s on the way, I just don’t think it’s a sure success so it hasn’t been a priority for drug companies to put money and resources into.