Natural monopoly
This sounds like a natural monopoly to me. In a natural monopoly, there are high costs to entering a market, and the size of the market is sometimes not that large. So it's that much harder for new entrants to enter the market. Not impossible, just more difficult so you tend to have fewer if not a monopoly then fewer competitors.
The standard practices in an illegal monopoly... before Standard Oil was broken up (the Sherman antitrust act was basically written originally to break up Standard Oil, who was very anticompetitive.) Two common practices they had to maintain their monopoly was to drop prices in an area with a new entrant to below costs to put the competitor out of business, then jack prices back up. And order capacity on trains, pipelines (if they had them that long ago), etc., EVEN if they weren't planning to use it, to prevent competitors from getting access to transportation for their oil.
They just got going launching their constellation first, and have been launching 'em at a rapid clip, so they have the most satellites and customers. Using the "Standard Oil" tests, they're bringing in $6.6 billion a year in revenue from a constellation they expect to cost $10 billion total to build (the $10 billion was from 2018 so this is probably higher, but still..), so I imagine they're turning a tidy profit (they're not selling below cost to lock out competitors.) And these constellations are all using different altitudes etc. so they aren't taking up orbital slots etc. that competitors need to operate in; Amazon's getting launch capacity from SpaceX so they aren't being anticompetitive by not selling launch capacity to their competitors.
That said -- it's certainly worth the FCC looking in to. It makes sense to take a look at anyone that has like 60, 70% of a market. I don't think they'll find anything, but they can let competitors make comments and see if there is anything worth looking into.