We should not confuse explorers with tomb robbers; a person who explores may have different goals, including finding a fortune, but keeps within the framework of a certain type of ethics; it is a leadership problem.
The tomb raider is simply a thieve who takes away things that belong to others. Thorough history we can find many cases of tombs that have been robbed, sometimes more than once because of their impressive contents; we can assume that some of the raiders involved may have become extremely rich, but in general, If caught they would have suffered terrible punishment, as it was customary among the cultures that used to deposit valuables underground as part of funeral rites.
That, indeed, did not stop some bold individuals, and some of those tomb raids required a lot of work and risk; however, regarding the kind of labour required to open them, there is something curious. In Nazca there is a royal tomb which was excavated about 30 metres into the ground; when it was studied by archaeologists, there was little left.
It is evident that it was sacked long ago, but not thorough a tunnel or passage found by the robbers. The grave was actually excavated from ground level, an digging 30 metres into the soil, especially without machinery, is something that takes some time and it is rather difficult to hide.
The most likely conclusion is that these robber had some sort of political or security cover-up, because this tomb is located in what was a cemetery for the elite; it was holy ground so to speak, and such excavations would not have gone unnoticed unless some sort of security apparatus or political cover up was developed, and that required the participation of the local leadership at various levels.
The history of ancient Egypt also provides us with an example of what was going on; there is a written story of an even that took place in Thebes, and started with a trial in which a relatively insignificant tomb raider confesses his crimes, but at the same time and without much to lose, he named some if his accomplices.
The problem was that his accusation included the names of very powerful and important individuals, such as merchants, military commanders, one or two judges as well as high priests, and on further investigation, his allegations proved true. He and others were eventually impaled; not so in the case of some high ranking officials.
But robberies are not limited to tombs; archaeology is a science that developed a code of ethics only recently, and up to the twentieth century, archaeologists just thought and assumed that what they found was theirs, regardless of any other consideration. If you just visit some museums in Europe, you may be able to see what in fact is the produce of plundering, piracy and robberies.
The British Museum is a fascinating place, but the pieces of Athens' Parthenon that are in exhibition in London were really purchased from the Turks, who sold them at a time when they were occupying Greece. The Greeks have claimed those treasures back, but it seems that the British are suffering from some sort of ear problems, for decades.