Not sure it's so rare. A large number of group chats will have people in the same area. For me it's the vast majority: family chat, groups of old classmates or flatmates are mostly in the same country, work chats too... I can think of one exception where a group member will consistently be hitting a different Cloudflare node from everyone else, but for everyone else, every time I send a picture into a group chat the caching will save traffic