Really don't understand what "unacceptable" even means in this context. It is perfectly acceptable for a company to control internet access.

More to the point though, what is this cheap and easy domain scoring system that does a better job than a blanket ban?

The best domain reputation provider, DomainTools, definitely isn't providing their data for cheap, nor is it always the fastest. We pay a substantial amount to them for thousands of requests a day, something we reserve for enriching actual security incidents, not because someone wants to go to catparty.foobar or whatever.

Unacceptable for who? It's definitely more than acceptable for a lot of people.

Sure, but blanket bans are even cheaper.

You say this as if the people implementing TLD blocks even understand what the term scoring system means

They really aren't when you are operating at ISP scale. Especially when there are 20+ years of evidence of said scoring systems being abused until they calcified into the mess that is modern email hosting