Most likely Google is trying to protect its autocomplete, as well as its organic search results, from being overwhelmed by an enormous flood of lies and misinformation being spread all over the web.

I would be surprised if autocomplete doesn't have anti-spam baked in.

I have a more sinister view of auto complete. It funnels visitors to keywords that more advertisers are bidding for.

There are only a handful of people at Google that know what actually is going on. The rest keep to the company talking points.

The principle of auto complete is broken. It fails in the discovery ability. It can only tell you what everyone else knows and will steer you into already known, popular aspects of your search. It's skewed. It has to be. Instead of assuming it knows nothing, it will guess what you want rather then considering the autocomplete doesn't have info on what you're looking for and actually not fill in anything. Imagine that! Can't autocomplete because not enough data? That will be the day to see admittance of shortcomings. It's shallow and wow, it sure can create a filter. Perhaps it's the next ad frontier, not sure. I've discovered the shortcomings of it lately. The issue is that it needs data and it takes from what's already there which does not work on anything new in this world that not everyone knows about. Shame really, but whatever.

Autocomplete is also a source for researching keywords when writing blog posts and articles. I've also used it for PPC keyword research.