Not because of adat. People make business out of funeral. Paper house, car and etc does not really cost much in term of material. Yest in small town people don't die daily unlike big city. This generate more money.

I don't know if land is provided but govt but most of funeral grounds are "tanah wakaf". People donate their land for public use, like they can wakaf the land for cemetery use, wakaf the land to build mosque, etc. Lands that are wakaf by individual cannot be changed or taken by govt. This has also has become an issue too when the land end up in the middle of commercial area. There were discussion about it and I did not follow up what is the outcome.

I can say after 3rd or 4th generations, no one probably visit the grave during Qing Ming. Some got children migrated to other countries. Who would pay for maintenance if relative cannot be traced anymore? In Muslim case, those old grave they will reuse for new body. The remains (bones) of the previous "dweller" will be moved to area that dense with other bones (buried much close to each others) to create more space. That is why it is cheap.