Didn’t notice, or didn’t care? Indie was most active when I think the latter was still most common. See: every ancient history exhibit in a major western museum (outside of maybe Italy) ever.
Ah! But they gave the order to clear the bridge, were sealing the hatch and it looked like it was going down as the crew from the freighter cheered him on.
And I think Duct Tape is a more cromulent hypothesis.
There’s a snippet of film made whebn they were shooting Indiana Jones and the Last Crusade that shows Harrison Ford using a stapler to staple his hat to his head (“There! That’ll keep it on!”)
The stapler was really empty, of course. I hope.
So, while they were searching for the cup that gave eternal life, they just happened to find another cup (or cups?) that instantly killed the drinker?
Perhaps they found it by following the clues on a necklace that said “Don’t DRINK water FROM this CUP, please. NEVER, or you’ll DIE!” in a toroidal spiral but they could only decipher the bolded words from one side. 
Obviously, they’re silly, but you could plausibly make a sunlight-activated death trap with a lens carefully focused on a thin line holding just enough weight to unbalance a giant potential-energy storage device with a lot of potential energy to loose.
Not sure how you could make a dark-activated one that wouldn’t just go off at night, though.
Magic. It exists in Indy’s world.
“Any sufficiently advanced technology is indistinguishable from magic.”
The Incas were instructed by space aliens, of course.
The Ark is also an example of alien tech.
Don’t release jailed Rigelians!
As for lack of provenance of Indy’s artifacts: How important were niceties in 1930s academia? Until non-invasive imaging, wasn’t human archaeology glorified tomb-raiding? I don’t see Indy returning with soil samples.