There’s a lot of speculation; Chinese Agamas read those parts more carefully, showing Buddha asking his Aunt to hold off ordaining, and to shave her head and wear the robes until the time is right. Pāli version seems to be heavily redacted at some point.
It’s a complicated history. In India, at the time, women were seen to be sort of properties of their fathers or husbands or sons, whichever applicable. The kind of complete culture makeover that requires to allow women to ordain, would be far too impossible even for Buddha.
However, Bhikkhu Analayo argues, that the rules were set out not to restrict the nuns per se, but to keep them safe from rape and other misdoings. After all, with such rules set in place, they could show the outside culture that the Monks were the guardians of Nuns, and anything they did to nuns would be met with the Monks’ retribution. Without such assurances in place, a fatherless / husbandless woman in ancient india would be an open invitation for false behaviours. Is it really so different today in some parts of the world?
I suggest you read Gotami section of Bhikkhu Analayo’s Daughters of the Buddha for a more nuanced view especially in light of chinese canon.
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I should note that Bhikkhu Sujato has an even more different interpretation. He argues that special training rules were set for members of Buddha’s family, because they were often prone to cause trouble and ask for special privileges. In just about all cases, rules for Buddha’s immediate family are even more harsher than what’s required of general monastics. Gotami’s rules seem to reflect this idea.
A support for this view comes from studying various poems praising nuns. There are a few nuns throughout the canon that are praised highly by others, especially fellow nuns, for being foremost in dhamma, for being excellent teachers, for having exceptional conduct. Gotami, interestingly enough, has no such praises attributed to her. For someone who spearheaded the entire nun order, nuns didn’t think it was important to mention their supposed “leader” at all.
While I agree that this is a peculiar thing indeed, I’m not sure I agree with this interpretation per se, because again, Chinese Canon (which seems to describe the event in more detail and without anachronisms of Pāli edition) seem to support Ven. Analayo’s perspective.
Either way, it’s a good case of canon being a guide and inspiration on our path and not a set of doctrinal teachings. We should apply our reasoning and heart to the matters and draw our own conclusions.
