They attend constant flashes and are in premium EC clubs as well. At their really high stats, they only need to do one or two hits on a party to get max drops, so they can get tons of drops by just hitting once on LBH on premium parties. That adds up to a lot of drops per one full regen. If you're doing that on dozens and perhaps over a hundred EC parties a day, it really adds up. Sometimes opening hunt boxes helps too especially if they're after a box avi, but mostly it's drops directly from partying. It takes a lot of work to coordinate attending the flashes and EC clubs to ensure you're getting that one hit in right before the party ends. T10 is particularly brutal.