Different bubbles are a visual indicator whether the messages are encrypted.

Apple is a good faith participant in that they support a fallback to the texting standard supported by every mobile vendor.

It’s not bad faith on my part when you brought up WhatsApp. Sure they don’t have blue but bubbles, but that’s because they don’t support an open standard at all, they don’t have an inclusive mode at all, they only support their own users on their own proprietary protocol.

Most importantly I don’t see how it’s Apple’s responsibility to push mobile vendors to modernize. Blame them if vendors were modernizing and they pushed back