Global cellular operator revenue is approx $1T. They have put their toe in the water with direct-to-cellular support for starlink, and have bought spectrum to improve this. I'm sure they basically want to offer cellular to everyone in the world and get a good chunk of that $1T. Maybe they want 20% of it? Sounds crazy, but China Mobile, Verizon, and Deutsche Telecom each have 10%. Sounds it's not so wild that they can grab a big chunk, especially if they can find new customers that are not already connected.
And of course they can also continue to grow their broadband internet access business.
I suppose they will likely start putting cameras and other data sensors on the satellites so they can sell other data for mapping, positioning services, agriculture, weather, etc. The incremental cost to add this to the platform will be almost nothing compared to existing systems.