Here’s what’s going on. Putting the genderless creatures aside, the creative team works hard to make sure that of all the remaining creatures pictured on cards in sets half are male and half are female, just as occurs in real life.
That includes legendary creatures. They are half male/half female, but people are so used to seeing males taking up a larger portion of space in pop culture that half female feels like a larger portion than it is.
For example, there was a big issue last year about how “all” the Pirates in Ixalan block were female. If you went back and counted though you’d find that it was half and half.
This is yet another reason proper representation in entertainment matters. When women are half of a group in the real world, we don’t want it to feel “off”.