When I worked at a company that offered free lunch, the company used it to help build rapport and camaraderie among the coworkers. It's one time during the day when the entire team can sit down and eat lunch together and get to know about each other, which is not possible through Slack nor via meetings.
I stopped bringing my lunch to work and go out to eat specifically to get a break from my coworkers. Not that there is anything wrong with my coworkers, but I really enjoy the alone time in the middle of the day where I can just sit back and read.