I think the thinking is that if you put in fast and frequent high capacity corridors, that those corridors will atract development and high denisty residential and commercial developments will estbalish themsleves around the stations. Thus in addition to serving structures that are already there (which is very difficult iof they are spread out) you are also catalyzing future development which will be more transit frienldy.
Government doesn't get it. You buy up the vacant land or buy options on it in secret around where you are going to put up the stations and pay for the transit with the profits when selling/leasing the land. Government announces where they are putting things then after everyone has bought up the land, they pay the inflated price for it. And if they do happen to own the land, the politicians make them change the location so their buddies make the profits. Brightline is probably buying the land nowaround their future stations on the way to Orlando or selling the information to local community insiders in exchange for certain rights, easements, or other considerations. [Cynicism off]