There is a shift towards cremation in the US http://en.wikipedia.org/wiki/List_of_countries_by_cremation_..., though seems to still be eschewed in the south. I don't know if there is any Baptist, or other religious teaching against cremation, or maybe it just has to do with cheaper land.
In Christian eschatology, one day Jesus will return and the dead will rise from their graves. For many people cremation seems incompatible with this, although one imagines a benevolent deity could just as easily reconstitute people from ashes, scattered or not. Then again a lot of religious people think this mass resurrection is going to be a pretty selective affair so that it's important to have the right address even after you're dead.
At 2 square meters per grave in densely populated areas they're going to sooner or later have to bury people stacked if they don't want the dead to crowd out the living.
But then there are family crypts with 4, 6, 8, 12 bodies interred pulling the average down. Not to mention the number of people who have been interred and then the cemetary later moved because it was on land deemed desirable to the developer (and of course a standard trope of many horror movies). So I doubt the dead could "crowd out" the living but they could certainly end up stacked in a cave somewhere far away from their original burial.
It varies. There are sometimes problems with private or small cemeteries that are run by an association running out of funds (or the association can end up with no members left).
A search for "cemetery disrepair" returns lots and lots of local news stories.
Even as a simple matter of logistics, I've often wondered - why don't we bury people vertically? About the only downside to it would be in the extremely rare case that exhumation is needed, which would have to be a (literally?) one in a million event?