It's a hard problem. I think there's a simple observation that helps explain why it's going to be so hard (the article hints at this without saying it): a healthy adult man is, more or less, fertile. At all times. If a adult man is infertile--if him having sex can't result in pregnancy--there's something at least slightly wrong with him.

By comparison, an adult woman is often infertile--three weeks (ish) out of every month, or whenever she's pregnant, she can't get pregnant.

So it stands to reason that it's harder to produce male hormonal contraceptives: we can (at least sort of) fake healthy-but-infertile states of women, but there are no such states for men; we have to construct one from whole cloth, so to speak, and that's much harder.