Why does the Supreme Sangha Council not allow women to be ordained even there are as many as 6,000 abandoned temples and the number of monks falls down to only about 80,000 these days? Buddhism in different countries allows women to be ordained except in Thailand, Cambodia, Laos, and Myanmar. How about allowing women to be ordained and stay in separated temples (from the monks’ ones)?
It is not the Supreme Sangha Council but the monastic disciplines that controls the rules for women having the will to be ordained. They have to come to live in the temple, under the same roof with the bhikkhunis (Buddhist nuns). They have to wear only white garment and practice the Eight Precepts. This step can take from 6 months up to 6 years. The bhikkhunis will evaluate their behaviors to see if they can move on to the next step, becoming samaneri or novice nuns. Then, after that they have to prove themselves by following all the disciplines taught by other bhikkhunis until the bhikkhunis agree that they are ready to move on to the final step, taking bhikkhuni ordination. At least 5 bhikkhunis need to be in a meeting to decide if they are ready or not. Then, the bhikkhuni who will give ordination to them will have to take them to take the vows of a bhikkhuni in front of other bhikkhus (monks) so that the other bhikkhus acknowledge that the samaneris have their pure intention to take ordination and ready to pertain their monastic lives by following the basic Theravada code of discipline consisting of 311 rules for bhikkhunis.
That is why Thailand has never had any bhikkhunis since the beginning of Rattanakosin era. In Ayutthaya period, bhikkhunis might have existed but were taken away as hostages by Myanmar until none left.
Because of the monastic disciplines, as a result, we do not see any woman being ordained and becoming a bhikkhuni in Thailand.