Actually, the word translated tombs, mnemeion, actually means tombs, sepulchres, or graves or any kind of memorial. It's the word from which we get our English word mnemonic which is something we use to aid our memory.
Only the rich could afford the kind of burial we associate with the word "tomb". Most people were buried in the earth or in caves. Often, the bones from which all of the flesh had disappeared were collected from a tomb or grave and put in ornate boxes called "ossuaries."
So, the answer to your question is that burial practices have not changed much and then, as now, what kind of burial place you were given depended on your wealth and/or status.
I hope you have found this helpful.