Some folks don’t get much value out of Sealed Chests, since their ships are effectively finished. In the Nimbus Wilds specifically, it’s a complete chore to get them down.
If I had to guess, it might be because of somebody doing a Mythical or Lost Treasure Chart; pirates from the second spot onward seem to only spawn when picking up the Sealed Chests, so they leave them there for an easier time. Main reason I say this is because one time I picked up a pair of abandoned Sealed Chests, and ended up getting pirates to spawn on me immediately after.
Sealed are useless for people doing lost/mythical charts and it’s a waste of time to reposition the ship or constantly turn back for more sealed, especially when you get 4+ sealed per chart.