People Who Buy In Low Density Neighborhoods Like Low Density Neighborhoods

That's not true of all them, of course. Some might not have any other affordable options and some might buy into a neighborhood because of a specific amenity that neighborhood offers (like school districts). But a lot of people live in those places because that's where they want to live so it shouldn't be especially surprising that residents of such places are happy with the status quo and don't want things to change. In desirable areas, restricting density keeps home/land prices up as well for an added bonus. But as regions grow in population, that means the only way to develop is by pushing farther out, and when you have a scarce resource like a major transit system stop, limiting development around the station means the transit system will get less use than it otherwise would, increasing congestion on roadways.