I'm 90% certain Stripe has had a few fly by night calling card companies sign up with them, and gotten burned when the calling card company gets a ton of chargebacks for not delivering everything promised.

Thus, a blanket ban on Telecom and anything vaugely related (like ISPs). Certain flagship clients like Twilio get a pass, but smaller players like SignalWire, Telnyx, Teli, etc do not.