You are not everybody else. Some people are very busy and use their lunch for all sorts of things: Time to read a book. Time to run errands that couldn't be taken care of during the previous or coming evening. Time to go home and see the cat. Time to go home and do chores. Time to go home and make food that you want to eat! The list goes on. It is my time, not anybody else's. If the group lunches are so wonderful, friendly, and relaxing, then people will show up to them, but anything approaching pressure to do so is patently absurd.