> Does being rejected by cliques at lunch make your experience worse than be rejected by cliques in other activities at work?

Fair point. I'd say the frustration comes more from the double-talk of "look how inclusive our workplace culture is: everyone eats together in the cafeteria!" The company admitting "we don't have any norms around lunch; everyone is on their own" would not be an objectively better experience, but at least would be honest.

Another option would be to have more official team, group, or project-based lunches, rather than a free-for-all, where specific members of a team privately invite other specific members of a team.

I don't mean to turn this into a rant, just adding a data point :)