Federal practice means the map is not the constraint
A firm's reachable market is far wider than its county, which changes what content is for and who it should be written to.
Because the practice is federal, a firm can generally represent clients located well outside its own city, and a great deal of the work does not require anybody to be in the same room.
That inverts the usual local search logic. Ranking in your own metro is worth something, and it is a fraction of the available audience rather than the whole of it.
The content that reaches the wider market is about the process rather than the place. What a particular application involves, what the requirements are, what the stages look like and how long things generally take.
It also means competing nationally, which is harder. The firms producing thorough process content are doing it for the same reason and there are more of them than there would be in a local category.
Being clear about where you are licensed and where you practice still matters, since immigration work frequently intersects with state law questions and clients should not be guessing about scope.