People being hacked since the last Server Check.

Going with your hotel analogy, imagine if the hotel had designed their own swipe-card system for the locks on their doors. A few robbers figure out the method used to create the cards, and then create their own cards and systematically begin robbing hotel rooms. By the time the thieves are caught, hundreds of rooms have been robbed/ransacked. What's a business owner to do? He can't exactly replace the items easily because it's an undue burden on the company. At the same time, many of these goods have no value or its value is heavily relevant on an unstable market force that is the Maple economy. How could Nexon possibly reimburse everyone's accounts? While doing database inserts doesn't sound time consuming, the amount of digging required to determine that the player was affected by a hack and their compensation is incredibly time consuming.

This is what a class action reimbursement is for - Everyone in the affected class is given an averaged restitution of expected replacement value.
Mabinogi for example was rolled back 5 days earlier, the restitution? 20K NX (actual prepaid NX, not credit) and a day of *5x* plus a few other perks.

Clearly they can handle the concept. All they really need to do is determine who falls into the effected class and determine a compensation that would be considered fair to the majority. If they really want to be nice they could deal with the ones who don't find it fair on a case by case basis after having weeded out 90% of them.