Gps is free to use. Running your own gnss service requires an atomic clock and possibly separate transmission hardware, which is possible, but adds cost, volume, and weight.
According to [1], “[o]ne of the current generation of GPS satellites (Block III) weighs over 2,200 kg (4,850 lb), the weight of an average pickup truck. The body of these satellites are 1.8 m x 2.5 m x 3.4 m (5.9’ x 8.2’ x 11.2’) in size”. In comparison, “the current V2 Starlink satellite version weighs approximately 1,760 lbs (800 kilograms) at launch, almost three times heavier than the older generation satellites (weighing in at 573 lbs or 260 kg)” [2]
According to [1], “[o]ne of the current generation of GPS satellites (Block III) weighs over 2,200 kg (4,850 lb), the weight of an average pickup truck. The body of these satellites are 1.8 m x 2.5 m x 3.4 m (5.9’ x 8.2’ x 11.2’) in size”. In comparison, “the current V2 Starlink satellite version weighs approximately 1,760 lbs (800 kilograms) at launch, almost three times heavier than the older generation satellites (weighing in at 573 lbs or 260 kg)” [2]
[1] https://novatel.com/an-introduction-to-gnss/basic-concepts/s... [2] https://www.space.com/spacex-starlink-satellites.html