The second situation is that in some places, there will be such a custom that no monument will be erected within three years after the grave is built.
The third situation is that some graves are very old, especially those of the older generation. Many of them only know a general location and know nothing about the specific situation. Many people don't know who is buried in the grave, let alone what monument is erected.
The fourth situation is that the general monument is a matter of paying attention to feng shui. Many people will choose a suitable day, and some even invite a Feng Shui gentleman to look at the location of the tombstone, the surrounding environment and the specific time.
Another important thing is that many people now choose to carve epitaphs on tombstones, and epitaphs are a more formal and serious matter and cannot be sloppy. Anyone who pays attention to them will seriously find someone to engrave it, and it will take some time to write an epitaph until it is engraved. In particular, carving epitaphs requires a certain amount of manpower and material resources, so we have to wait for the tombstone to be carved slowly. So there is a certain waiting time in the middle, so there will be a certain delay in erecting the monument.
The last one is geographical factors, because rural areas are not like cemeteries in cities, and rows are very neat. Without a tombstone, I don't know which is which. But the countryside is different. The countryside is big and mountainous. Even if you don't set up a monument, you are not afraid that you can't find a place.