It's mostly because people have a priority of things to get. That's nature with weekly lockouts.
Assuming you're in A9 and want a bolt and would take a chain as booby prize.
The loot is: pedal, pedal, chain, bolt.
Now you would pass on the pedals and roll on the bolt first. If you hit a 90+, you sure won't roll on the chain before everyone else rolled on the bolt.
Because if you roll on both you may end up with the chain, instead of a bolt just because everyone rolled/passed on the chain first.
Now there's this other person who needs a chain and would take a bolt as booby prize...