You're misunderstanding the situation and reading malice into teenagers who are living in a world of decisions that were made before they were even born.
It's not "small stuff", it's the entire medium through which the conversation happens. It's the entire thing.
Do you "cut" your mom out of your group chats with your coworkers? Do you "cut" your coworkers out of intimate chats with your partners? Of course you do, because people maintain multiple overlapping group chats.
In group chats with your blue-bubble friends, they will be easier to read (because of the shades of color), media quality will be better, you can add more people to the group chat after it's made, you can text people from your iPad or Macbook, you can text people over WiFi even when you don't have service. When each text used to cost money, it was also a huge deal that iMessage (on WiFi) was free. This is on top of all the other chat features like playing games, pins, etc.
A lot of these limitations are intentional so that Apple can make more money, some of them are just limitations of SMS / RCS. But the point is that this is not the kids faults, this isn't bullying.
I am not misunderstanding the situation. If you omit me from a group message with our circle of friends because of the color of my speech bubble, you are not a real friend. Full stop.
Just the phrase "blue bubble friends" strikes me as absolutely wild, foreign and ridiculous. But, I admit to being almost 50.
The "blue bubble" just signifies someone's using the iMessage platform, and we still have multiple messaging platforms nowadays. Think of it like "Usenet friends", "IRC friends", "ICQ friends", "AIM friends", etc.
I don't know you, of course we're not friends. I addressed this in my comment. There are group chats you are part of and ones you won't be part of. Most people maintain multiple different overlapping group chats.