That's just the initial system. And there will be, say, 30 satellites in view at any one time, giving an aggregate of 600 Gbps. At a typical 100:1 over-subscription ratio, they should be capable of serving almost a million customers per region (~500km diameter) at that speed. At more reasonable 10 or 100Mbps, it's on the order of tens of millions of customers in a region.

But that's just the initial constellation. SpaceX plans to put 12,000 total satellites up, with the VLEO ones having much higher throughput. Idea is to replace them every 4-6 years with faster throughput.