I work at the sister company, so things are pretty similar. We have lunch together and everyone participates (although it's not mandatory) simply because we all

I work at the sister company, so things are pretty similar. We have lunch together and everyone participates (although it's not mandatory) simply because we all have our own offices, if we didn't have lunch together I wouldn't get a chance to talk to my coworkers face to face at all in a day. It's a huge contrast from when I worked in an open-floor environment and thought of lunch as my "alone time".