They own a lot of those regional competitors that are less well known.

They play in both market categories, they sell it at higher margins with twilio brand.

Then sell it again, at lower prices from more regional less known brands.

This. They're great for small/mid-sized developers, but they price themselves out once you're doing billions of messages a month. At that point companies start looking at aggregators one level down (i.e. closer to the carriers or raw SMTP).