SpaceX has 3 direct competitors in similar orbits. All 3 have global (ITU) regulatory approvals, but are behind on building and launching things.
Simple: to provide maximum speed to the end users, you want a large amount of small cells so you can better use the allocated frequency spectrum. However, launches used to be really expensive, so operators had to go for high orbits covering large areas - Iridium, for example, cost 5 billion dollars to build for 77 satellites, meaning a cost per satellite of ~64 million dollars (hardware+launch).
In contrast, SpaceX is at ~250k-500k dollars for the satellite and anything from 30-60 million dollars per launch of 60 satellites, so total cost of ~750k-1.5 million dollars per satellite [2]. That's a whole order of magnitude less cost than Iridium.
And on top of that, SpaceX's lower orbit also means better service quality due to lower latency and better signal quality. Established satcom providers physically cannot compete with that.
[1] https://en.wikipedia.org/wiki/Iridium_satellite_constellatio...
[2] https://www.nextbigfuture.com/2019/12/spacex-starlink-satell...
It is all about efficiency. You have to build and launch thousands of satellites, and no company other than SpaceX has driven down the cost of those two things enough to make it feasible.