It’s all the other features in iMessage that android users “ruin” in group chats. Things like read receipts, typing indicators, reactions, animated/spoiler text messages, sending media in full quality, etc… A single android user is enough to downgrade an entire group chat, so apple users tend to be a little bit resentful.

It’d be a little bit like if one person on a Discord server disabled all the fun parts of Discord, and it killed the functionality for everyone on that server. Now nobody in the server can add fun little reactions to messages, or start threads, or send embedded gifs. All because that one person decided they didn’t like it.