The best explanation of why people are compelled to take items from wrecks is best explained by reading a book like The Last Dive, Fatal Descent, Shadow Divers, or other books of the deep shipwreck diving genre. These provide a lot of insight as to why people want to bring things back from wrecks. Back in the 1980s, some folks including a number in the California Wreck Divers were self-described "brassaholics", compelled to remove items from vessels just because they could, regardless of whether or not the should.
I think this practice has morphed, for the better, into movements like tech diving and other pursuits where the achievement of "being there" and "not bringing it back." But some people are into collecting stuff (just look at all the reality shows on pawnshops, storage unit auctions, and pickers and you see what I mean).
The paradox that has always confused me is that through their actions, the people who take stuff deprive anyone who comes after them the thrill of discovery, the thing that the savlor so highly prized in the first place.