Stop walking on the grass..
It creates a path, so try to stay on the same path when you walk around town. If you run everywhere, it will deteriorate everywhere you step. I think it comes back if you don't play for a while...
Well that sucks.
I hadn't played for a few months and than I came back, but the grass was still gone in some places. I have to run everywhere, don't have a ton of time to play unfortunately.
Thanks for answering, though.