Not all. It’s very much possible that there have been just as many enlightened women as men. But it is also true that most recognized masters were men. It has something to do with male ego.

As I mentioned in other answers, most teachings don’t come from a place of complete realization. In complete realization, the emotional desire to help is no longer there, it is seen as an empty pursuit, so teaching might happen or it might not happen, but it’s of no consequence. It can be a job to make a living, a lifestyle, or a genuine enjoyment of helping others, but there’s no need. No need to express yourself, no need to help, it does not bring more pleasure or fulfillment than other things in life.

But on the way there, the desire to help everybody arises in maddening intensity. As Osho said, “Every Buddha tries to help people, it’s unavoidable”. Buddhahood is an unimaginably exalted state, but it still carries a subtle hint of ego.

So, a male ego (what little left of it, to be exact) wants to announce, it wants to help, it wants to teach. This desire arises out of compassion. The compassion manifests itself as leadership, he says “Listen to me! I know the truth, you have no idea how beautiful your life can be, I can show you the way!” This often times is perceived as arrogance, but it’s not arrogance, it is his tears for humanity. It’s how he expresses his love for you. He wants to destroy your ego, because he knows your ego brings you suffering. If he’s not given an opportunity to teach, he will cry his tears in solitude, and will disappear as a teacher forever.

For a woman, when she finds love, love is enough. She will become love, and she will spread love, through compassion and understanding, but in a quieter way. She rarely has an ambition to help thousands, her way is that of acceptance, not of destruction. Her love blossoms over the entire world, just like that of any man who attained, but she will express the same love differently.

It’s not a rule, just a tendency. Everyone’s ego is unique and even though gender is a big part of it, it is not defined by it. Just like there are many men who never announced, never taught, and died completely unknown, there are many women who announced, taught, and were successful at teaching.