> because B2B where there's an existing business relationship are normally excluded from spam laws.
That's not just B2B, but that's part of the definition of “unsolicited”, it doesn't make the commercial part is a red-herring, either in general or in the context of this thread, which did not involve either a pre-existing business relationship or, since you unnecessarily called it out as relevant, a B2B interaction.
> The UBE (unsolicited, bulk, email) definition is the one used by most blocklists and filters
That's because “bulk”, unlike “commercial”, is easily detectable. (And also because because bulk has the most impact, because, bulk.)
> and ISP AUPs.
Virtually all ISP AUPs include prohibition on unlawful use which includes violations of laws concerning unsolicited commercial email.
The "bulk" definition is more widespread and is the definition that's enforced more often. So, mentioning "commercial" is weird because most service providers don't care whether it's commercial or not, they care whether it's bulk or not.
More commonly, unsolicited/unwanted commercial email, see, e.g.:
https://www.consumer.ftc.gov/articles/0038-spam