As to the Egyptian scenario:

When people are repressed by heavy religious superstition...not to mention the real threat of instant and agonizing death, it is much easier to keep them "in line." Superstition is a valuable tool.

When you had threats against desecrating and/or robbing a tomb like :" May you be seized as a wild fowl", I imagine most terrified citizens were more than happy to stay away.

I also think that it is suspected that when some of these thefts took place, it may have been at the bidding of higher ups (such as priests). They could enrich themselves and engage petty thieves to take all the chances.