>>If Leave this Conversation is grayed out on your iPhone, there are only three participants in the iMessage conversation, and you can’t convert a three-person iMessage conversation to an iMessage between two people.
>> Even if you delete the entire conversation from your iPhone, you will be added back to the group the next time someone sends a message. The only way to leave a three-person iMessage conversation is to add someone else to the group so it becomes a four-person conversation: Then you can leave.
Whatsapp does allow it and this nicely allows anyone to create a small personal note taking area: just create a group chat with anyone else and then ask that person to leave again.
Because it’s no longer iMessage, but SMS. The other phones are sending to everyone they think is in the “room”. So you’ll be re-added. You’ll just have to tell them to stop texting you.
