This reminds me of a conversation with an iPhone-using elderly relative who wanted to text friends in their retirement home:
ER: Why is it that when I send text messages to my friends they sometimes never get them?
Me: When you get messages are the bubbles green?
ER: Yes.
Me: Is there bad phone signal in this area?
ER: Yes.
Me: OK, that means your friends are using Android phones, so your messages are being sent by a method called 'SMS' which isn't very reliable, particularly when phone signal is poor.
ER: I don't really understand that. What I can I do to fix it?
Me: You and your friends could install an app such as Whatsapp or Signal and send your texts with that.
ER: No, I'm not installing an app!
Me: You could persuade your friends to buy iPhones.
ER: They won't do that.
Me: You could wait a few months and Apple will most likely activate a new system called "RCS" on iPhones which might make messages with your friends a bit more reliable.
ER: That's no good, I need to fix it now.
etc. etc.
Not that it is relevant to overall point, but this is the exact opposite of my experience. I've been in plenty of situations where it is impossible to make calls because the signal is so bad, but communicating with SMS has worked perfectly. As my signal gets weaker and weaker, SMS is always the last thing to fail.
Apple has made the correct set of trade offs. If you just want to send a text message and don't care about the particulars you can do that and you'll automagically get the best possible experience based on the best lowest common denominator protocol whether it is iMessage, RCS, or SMS.
And if you and your buddies are savvy enough to want more than that you can install Signal or Whatsapp or whatever.
But that baseline out-of-the-box experience for mobile phones has always been "if I have somebody's number I can text/call them using my phone's out-of-the-box functionality and the network sorts out the details."
I think it's kind of nuts to throw that in the trash and you don't appreciate what a huge step backwards that would be for most of the people who buy and use phones.
Also, would you not agree that out of the box E2EE is a huge deal!?
But the keys and key exchange protocol for E2EE have to be managed by somebody. Signal, Google, Apple, whoever.