Because it's a polite fiction that men and women are equally capable and expendable at warfare. Successful and enduring human societies practice traditions around warfare that reflect this.
> Sometimes I wonder if AGI (and the concept of a "technological singularity") isn't just "intelligent design for people with north of 140 IQ"
You're not the first person to express this idea, but it's pure speculation. There is obviously a possibility that it will be proved correct at some point in the future. But historically, very smart people have been ridiculed like clockwork for expressing ideas that were beyond their time but philosophically (and physically, eventually technologically) possible.
I'd be wary of adding to such sentiment. It also feels suspiciously like an ad hominem criticism, although in your case it's expressed more like a question. I think there is clearly something to the idea of very smart people having an intellectual disconnect with the reasoning of their closer-to-average peers (and hence expressing things that seem ludicrous, without considering how they will be received), but not one that negatively affects the quality of their deductions.
IMHO, the ideas of AGI and a "technological singularity" (let's call it economic growth that's extremely more powerful than anything seen up until now) aren't so different from earlier, profound developments in human history. The criticism of "smart people developing a blind spot" could have been applied equally to e.g. the ideas of agriculture and the following power shift, industry, modern medicine, powered flight and spaceflight, nuclear weapons or computers, networking and robotics.
All these ideas put the world into an almost unimaginally different state, when seen with the eyes of an earlier status quo. Maybe AGI is relatively different, it's hard to say without having lived in ancient Egypt. It's certainly qualitatively different, since it involves changes to intelligent life, but I'm not sure the idea feels much more alien than things we've already experienced.
Fun fact, there are places in the Western world where it is considered illegal to the same degree as photographs of children being abused. And ditto for textual descriptions of this fictionally happening. Scandinavia, for instance. Which is admittedly not famous for its uncompromising approach to freedom of expression.