As a programmatic telephone company, they're a possible (but not really probable) base for fraudulent spam calls. With KYC, and the fact that Twilio requires you call from a number you control, fraudulent calls would be easy to trace back to a person who could be charged for the calls. Much better than status quo, where it's very difficult to get to the originating phone account, and if you could, it's probably not really connected to a person.
Surely the overheads of any useful KYC are way too high for this to work? And basically nobody in this industry does KYC, so how do you propose that would meaningfully affect their interconnects?