You're right, but they're currently at what looks from the outside to be at pretty severe risk of losing their FCC spectrum license, much requires them to have a certain number of satellites by a certain date.
That, compounded by the fact that "their" rocket company (blue origin) is well behind schedule, makes it seem a bit foolish. If they weren't Amazon, trying to spend their money on another Bezos business, their absolute refusal to launch even their demo/pathfinder sats on a spacex rocket would look a bit suicidal...
Amazons entire company model is to create businesses that it needs for itself 1st, and then sell the excess capacity.
Why change now by using SpaceX?