Rules are only as effective as the mechanisms enforcing them - I don’t think anyone wants ads on Lemmy instances, but removal requires moderation tools and staff (volunteer or otherwise) to review everything that’s posted.
I imagine the problem we’ll see is as growth accelerates, post velocity will outpace moderation manpower - short version, you’re always going to have to do some blocking/filtering of your own.
A report has to be reviewed for accuracy, there’s still time and resources required. It’s not as simple as just blocking every post or user that has a report submitted against them. People abuse report systems all the time.