I have a theory on why male CASTs look like gundam robots while female CASTs look like beautiful women... other than PSCrew being horny.
What if male CASTs are CASTrated?
What PSO1 and PSU CASTs were confirmed to be all machine, PSO2 CASTs are able to use Techniques and this is explained that CASTs were once humans with extreme potent for photons to the point it's a deadly strain on their organic bodies. To save them, I presume their brains and some of their organic parts were placed into specially designed androids. So they're more cyborg than robot.
My guess the reason why female CASTs appear more human than the males is because they still have functioning organic uterus. That while mostly mechanism there is stilll enough organism in them to support life.
Males with exterior reproductive organs however maybe unlucky, that what's left of them inside the CAST is not enough to maintain healthy sexual organs, thus removal of them is necessary.
Whoever was in charge with turning humans into CASTs probably figured "The men can't reproduce so might as well make them all-out look like robots. Women however can preoduce so they will need to retain their sex appeal."
And just because male CASTs don't have their genitals doesn't mean they are all aromantic. Some can perhaps still form relationships with other CASTs or the other three -man races, they just won't have any sexual attraction towards them or capacity to feel lust (or maybe they can feel lust or a sense of horniess but it would be diminished without the testosterone produced by the genitals).
They will not be able to procreate, unless a healthy supply of their seed is frozen and stored somewhere.
It's my answer to why we don't see any male CASTs that look as human as the females do.
