Bearblog.dev keeps subdomains out of search indexes until it approves them, as a measure against hosting the sort of things that would get the whole system de-indexed.

My guess is that they are more successful at suppressing subdomains than at getting them indexed. After all, they are not in control of what search engines do, they can only send signals.

For reference, I have a simple community event site on bearblog.dev which has been up for months and is not in any search index.