It's largely because Amazon started Leo / Project Kuiper in the late 2010s when Jeff Bezos was still CEO of Amazon. Musk and Bezos both run rival spaceflight companies, and during this era, Musk and Bezos had multiple public spats stemming from:

1) Blue Origin & SpaceX competing for the same NASA / DoD resources.

2) Blue Origin using government processes to block / stall contracts that would go to SpaceX.

When Musk fired a number of Seattle-based Starlink execs in mid-2018, Bezos took them in to build a competing product. After Starship launched its inaugural flight and it was clear Blue was 10-15 years behind SpaceX, the rivalry died down. By then, Bezos had already stepped down as CEO of Amazon. Now Amazon Leo / Project Kuiper exists as an inherited project.