Sometimes, it was cultural values that led them to feel that their significant artefacts should be left where they are, where they belong. It's the other kind of public. Sometimes they just didn't think the things were that important, because to them they were normal, not exotic objects of study as they were to foreigners. If we're discussing Indy's era, it's mainly a matter of resources. The UK, France, and the rest made themselves rich and built academic institutions and funding structures for these kinds of expeditions. That wasn't available in other countries.