I'm not sure how long ago you sailed, but Royal Caribbean does now charge a table fee for going to Johnny Rockets (about $3.95 if I remember). Although it appeared that the charge was per person, we've eaten at Johnny Rockets on Royal Caribbean ships at least 6-7 times and were usually only charged one table fee no matter how many of us were at the table, and no matter how many burgers/fries/onion rings were ordered.

I understand this was initiated to prevent teens (and others) from hogging the booths all afternoon to just 'hang out'.

Additionally, I believe you also pay for the milkshakes.

As a repeat Royal Caribbean customer, you are given a book upon boarding which has coupons, including one for a free table charge at Johnny Rockets.