Sms was from a time communications weren’t done over IP, RCS or iMessage use the IP protocol, RCS could be implemented by the telcos but isn’t because , unlike SMS, it can also be implemented by anyone with a server with a connection to the internet but as RCS is an open GSMA telecom standard, it is implemented within all modem chips by phone makers, even Apple has a Qualcomm modem chip with RCS management included. I reckon it needs a few extra features in the basic standard such as E2E encryption, chatbot capabilities, malware and spoofing protection, maybe Google could help there as they have introduced those into their Message app and could disclose their code, but they are obviously trying hard to create a walled garden too… The solution could come from Meta as they seem pretty keen to advance on open communications (Threads interoperability with Mastodon is a demonstration of that policy)

Android users get to use the default messages app, with the whole e2e encryption, reactions, full sized photos etc… SMS is used for advertisements, and sending messages to iphone users… SMS is only used by old people for 2fa as 2fa apps usualy have superior security and are now systematically prefered by companies.

Both iphone users and android users need to download an extra app if they want E2E, full graphic images and videos, reactions etc…

Just as people aren’t content with iWork and usually download Office because it works the same and can be read with the same formatting everywhere.