I know that asking you to Google things is maybe a lot, but isn't the answer pretty obvious if you think about it for more than five seconds?
Roads are made out of what would otherwise be a waste product from refining oil, mixed with dirt. If you just leave it alone, it will basically just sit there.
Rails are made out of steel, which is both expensive and rusts. Tolerances have to be tight. And if you fuck about with maintenance in rail, you get a train derailment.