No these messages are not spam there either, because they are not spam period.
What you might mean is that the carrier's draconian probabilistic anti-spam system incorrectly categorizes them as spam. And that this causes a practical problem for Twilio, which lacks any recourse against said carrier's incorrect classification. In other words, a similar problem to what OP is complaining about, one hop away.
You're doing nobody any favors by elevating technical details out of their narrow context and stating them as an unassailable description of high level behavior.
Yet again you're just stating a technical description as if it implicitly justifies the state of things. Nobody here is confused about how Twilio can legally do this or how market incentives encourage them to do so.
We're discussing a higher level behavior and what ought to be. And getting a critical service pulled out from under you based on overzealous unaccountable spam filtering is certainly not what ought to be.
What you might mean is that the carrier's draconian probabilistic anti-spam system incorrectly categorizes them as spam. And that this causes a practical problem for Twilio, which lacks any recourse against said carrier's incorrect classification. In other words, a similar problem to what OP is complaining about, one hop away.
You're doing nobody any favors by elevating technical details out of their narrow context and stating them as an unassailable description of high level behavior.