Mods and admins need to feel that rush of power of hitting the ban button. Doesn't matter if it destroys the platform. Look at the mod log, it's disgusting.
I think it might be the Windows licenses that felt like an ad. It was removed from reddit I think so I can't confirm.
If the bot is unbanned, it should be easy to make a whitelist of domains, but even then there could things falling through the cracks (like sketchy 3rd party Amazon/Newegg/Walmart stuff). A whitelist would also not be inclusive of small platforms (like the Staples resale website where people can get legit workstations for 200), and would take a lot of effort to build if we include direct sellers (Dell, Lenovo, Samsung, Apple, etc).
Blacklist might be better, but it will not account for new domains where most of the ads/scam happen. So it would be high maintenance.