Presumably because they have a piece of legally binding paper saying they do? Changing the law to cut out the monopoly is the government reneging on the agreement they made with the monopoly to pony up the cash and presumably a tort.
The article says that that’s the status quo but Starlink aren’t ok with it. Not enforcing the law would also seem to be actionable under any agreement signed though. Finally, any precedent set here will make it much harder for the government to strike any other kind of deal next time it wants to encourage a company to invest.
I’m not saying break contracts, just saying there are usually sensible alternatives to exiting these sort of things that don’t involve just paying someone off.