While I'm certainly for building supertrains everywhere in an abstract sense, given limited resources it makes sense to improve transit in places which already have "transit oriented development" but maybe not quite as much transit as they should. Or, thinking about it from the other direction, a lot of improvements in "transit" can actually be achieved through improvements in land use, by creating transit oriented development around places which are actually well-served by mass transit, but don't have the appropriate density around the stations.
The point is that there are places which have high density and walkability but don't have as good mass transit access as they should, and places which have pretty good transit but don't have the appropriate level of density.
