I agree that Twilio blazed the trail, but much of what you mentioned is a known quantity now and can be replicated with less effort.
You don't need to be as good as Twilio, just "good enough".
While working with one carrier is easy, working with 5, 10, or 100 is a horrible pain in the ass. In addition, you need a compelling reason to convince higher ups in your org to sink $texas-sized dollars into this.. long before you can send that first message.
Uber is a special case as they needed coverage in countries that Twilio didn't support. Further, they had a ridiculous pile of money. Since they had to stand up the architecture anyway, adding the "easy" countries made sense.