They can't really lock or disable world visit to reasons stated; craft/gath density fluctuate heavily between servers and it's way too early into the content to take a drastic action as they need to see how the activity get to once the hype have subsided and players that came in rushing got their items and leave the content, leaving behind those leveling doh/dol, getting more scrip item or actively working on progressing.

One solution to avoid any future issue would be to implement an Effort Participation threshold and only allow players to participate in the event if they delivered at least a certain number of items (example 100 or 200 items sound fairly reasonable and easy to attain), that would drastically limit the leeching from inactive players to jump to other world when the event is up as they wouldn't have participated in the stockpile effort and allowing active players to be able to attend the event. It wouldn't prevent players from others world to visit and do the deliveries but it would kneecap attempt a lot as they'd have to farm across multiple world which would be time consuming to do so.

But in the meantime, deal with it as it's bound to calm down by next week or shortly later.