from someone who is not too long outside of high school and so maybe remembers this better:

imessage is specifically impactful because it doesn't exclude from individual communication as much as groups. you can still talk to your friends just fine but i remember being left off group texts because the experience is otherwise just so bad. can't add people can't react to stuff whatever.

what usually happens is there ends up being a second gc: 1 is ostensibly the "main one" with everyone in it and the unofficial second is with just blue bubbles. but communication usually ends up in the blue bubble one.

i will add it's not nearly so bad now, most people just do a snap gc but that wasn't the case e.g. 6 years ago.