Why Do People Group Message Unnecessarily?

This isn't about Group Message as a whole. I'm all for group message when necessary and convenient. I use it. BUT when the conversation doesn't pertain to the rest of the group, GET OFF THE GROUP MESSAGE. No one wants to hear their phone go "ding ding ding ding" only to read messages between two other people - especially people they don't even know. You know, like when someone says "Happy Thanksgiving or Happy Easter" to a group of 15 people, then your phone starts going crazy with dozens of greetings back and forth between a bunch of strangers? It's exhausting!