I've been back from my travels in the United States for a couple of days now. Weather is beautiful, the hermitage hasn't burned down in the meanwhile and there's a big pile of firewood delivered and waiting for the saw. Took my first dip in the Arrow River too, it's a short season for river bathing here, unless you're a total masochist, so I like to take the chance while it's on.
One of the stops on my journey was the Bhavana Society in West Virginia, for the monastic conference. This is an annual event for Buddhist monks and nuns of various traditions to get together and compare notes. It's heartening to see that the traditional monastic form of Buddhism is so well established in North America.
One development over the last decade or so has been the growth of women's ordination. There were three theravada bhikkhunis at the conference; the women's order is now pretty much established in Sri Lanka and making inroads into Thailand.
There was a presentation by Bhikshuni Thubten Chodron, an American woman ordained in the Tibetan tradition regarding the efforts to get the female order going in that school. I hadn't realized it was such a complex matter.
A little history; when Buddhism split into eighteen schools in the period after the Second Council, that also meant eighteen ordination lineages. At least three are still extant; the Theravada lineage of course remains unbroken, at least on the male side, as this is the only one of the original eighteen schools still in existence. The recent restart of the Theravada bhikkhuni order was seeded with Dharmaguptika nuns from Taiwan.
The Dharmaguptika lineage seeded the Mahayana orders of East Asia before it's founding school died out in India. Chinese Bhikkhus (monks) and Bhikkshunis (nuns) are ordained in this lineage; which interestingly enough, was originally transmitted out of Sri Lanka at a time when Dharmaguptika was present there alongside Theravada. This lineage is the only one that maintained an unbroken female ordination transmission.
The Tibetan monks are ordained in the Mulasarvastavadin lineage, at one time a very strong school in Northern India. Like the Theravadins, the female line was broken at some point. The recent small numbers of women ordaining in Tibetan schools have all been ordained in the Dharmaguptika lineage, like their Theravada sisters.
Now, it seems, the Tibetans are looking into the minutiae of Vinaya to see if there are ways and means to restart the Mulasarvastavadin female ordination, so that the bhikshunis will share the same samvasa (community for ritual purposes) with the bhikshus. The current controversy rests on the question of whether it would be legal under Vinaya for monks alone to ordain nuns.
This is all a bit more detail than most readers would be interested in, but is still a pretty rough simplification. So, whenever anyone asks why there aren't more female monastics in Buddhism, the answer is; we're working on it.