The total aggregate bandwidth Starlink will have when their entire constellation of satellites is deployed and the number of satellites that will be visible at a given location at a given time place an upper limit on the number of customers they can have even with overselling bandwidth.

In the US their plans are to be able to support something like 5 million customers. That's less than 5% of the number of customers Comcast has.

It really is by design meant for people in areas that do not have terrestrial broadband.