There is a record of a very frank conversation among senior monks in Bangkok regarding ordination, and this is one of the major issues. The problem they expressed is that, given that there are estimated to be twice as many sex workers as monks in Thailand, if bhikkhuni ordination were to be available, these women and girls would soon find they had other options, and would join the Sangha in large numbers.
This would mean that there would likely be soon more nuns than monks in Thailand; and they pointed a worrying finger at the situation here in Taiwan as an example of what can happen when things get out of hand, with four times as many nuns as monks.
The notion that it would be a good thing for women to have options other than sex work was not a part of the conversation.