Yeah, I was really surprised by this. Last year, I reported a number of people, who were trying to scam me (via Messenger messages related to Marketplace listings). Not only did Facebook did not see anything wrong with the accounts and scammy messages, I was flagged for sending useless reports.

I suspect that the report button doesn't actually cause any human to be involved in the process.

it (used to) in aggregate trigger human review (i.e. if many people report the same post). However, the humans who reviewed it were underpaid, overworked, and unlikely to have any context, so the output was not necessarily better than the automated system...