They wouldn't be graves any more.
For me they would be, if there were people buried there...
Since I was a kid I was taught not to walk on graves, not to step on them or walk over them, because that's disrespectful.
Maybe that's why graves in Poland usually look like this:
And not like this:
At the cemetery in the countryside where my relatives are buried there are all kinds of graves - made of stone or just a pile of sand with a cross, but they're always the size of a human and noone walks on them no matter how old and neglected they are. Some are clearly that old that probably there are no relatives to tend to them anymore, but still you know they're there, even if there's no cross left, because there's greenery growing on them surrounded by a path made by people who's been walking around it for years.
I would feel uncomfortable walking on a grass in such a park knowing that there are dead people lying there.