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).
What the hell are you talking about? In the past five years ISRO has launched 177 satellites for 19 different countries. I remember watching one for Singapore just last week.
The vast majority of those satellites are basically a joke. They're all tiny cubesats, and the entirety of their commercial space program in that period could probably fit on a single Falcon 9: https://en.wikipedia.org/wiki/List_of_foreign_satellites_lau...
