I'm no economics expert, but I gather certain industries are known as 'natural monopolies' https://en.wikipedia.org/wiki/Natural_monopoly

I don't know what the precise defining lines are, but I can certainly see how you'd make more money running an electricity cable to a home with no electricity, than running a second cable to a home that already had an electricity supply in place.

And Wikipedia says "frequently occurs in industries where capital costs predominate [...] examples include public utilities such as water services, electricity, telecommunications, mail, etc" - starlink does sound like capital-intensive telecommunications.

Of course, even if nobody cares to take on Starlink in the broadband satellite internet market, there are a bunch of incumbent cable and cell phone companies. So it's not like starlink are on course to an internet access monopoly.