Because they're more expensive and inferior? There's a reason that ISRO's only launches in like the last 5 years are domestic launches, and two launches for a competitor to Starlink that needed an alternative after Russia invaded Ukraine (and ended up launching twice as many satellites with SpaceX regardless).

The cost of launch on most of these projects is not the main cost component.

If you spent years and hundreds of millions on the payload, you are willing to pay more to launch on a platform with a very proven track record, like Falcon 9.