1. Some people are so far to the left side of the bell curve that they're going to be screwed out of a human relationship no matter what they do, and it's unkind to withhold sex bots from them just to provide increased motivation to the segment of the population that's still salvageable.
2. Society seems to have collectively decided that romantic intimacy, unlike food and shelter, is optional and that experiencing an absence of it should not entitle you to sympathy or support. Therefore, the kindest thing they can do is leave the autists alone so they can cope as best they can in peace.
UPD:
3. Replacing productive activities with substitutes like video games is obviously bad both for individual survival and for society at large, but what are the negative effects of being in a relationship with a fictional partner instead of a real one? You could argue the AI companies would have an incentive to exploit their users, but this is a thing that happens in real relationships as well!
Fertility might be a concern, but my understanding is that the current mainstream view is that the world needs fewer children, not more of them.