IIRC it can take quite awhile to get a headstone/marker made, and they may even have it - but waiting for better ground conditions to place it.
My father-in-law is buried in a small cemetary in New Jersey. I imagine nobody visits his grave either - except my mother-in-law was there visiting a couple years ago.
And the boat takes months to travel from China, through the Panama Canal, up to New Jersey. Shipping costs on a 500 pound Chinese rock must make up 95% of the cost, but that's how it's being done now. We can't even dig our own rocks out of the ground anymore.