Q: Why can't I leave a group message in iOS 10?

I recently updated to the first installment of iOS 10. There is a group chat in my messages that I no longer wish to be a part of. I can't figure out how to leave the conversation though.

i did the following steps.

1: Opened the message/conversation

2; Tapped the little "details" icon in the top right

3: I scrolled down but there is not a button that says "Leave Conversation"

it is very weird because I have another group chat that I am a part of and when I check on it, there is a button that says "Leave Conversation". I don't understand why one group chat has the button, but the other one doesn't.