> Any idea why they’d even bother implementing the interface, given it appears to be a step backwards compared to current options that customers have?

It's only a "step backwards" if you for some reason don't consider decentralized, standardized protocols implementable by anyone superior to centralized, closed-source walled-garden services.

"Anyone can implement a client" isn't the strongest argument when that's also true for most chat services as well. It's nice that the protocol is out in the open but it's effectively a service provided by cell providers and locked to them.

RCS could have been amazing as a general-purpose protocol for short datagrams that could be sent/received in areas where you can't get a data connection. It would effectively enable every chat app to work when the network is under load but carriers opted for the walled garden.

Or if you judge services on how well they work, not just on how "open" they are. To many people, just being "open" is not the be-all, end-all of whether something is better.

It is a step forward from SMS, although with many of the same drawbacks as SMS.