Eh, no one else is doing anything to provide support apart from Google either. Anyone else could do their own thing, no one is prevented from their own support. But very few companies and carriers even began to develop support for RCS, even after the Universal Profile. That is why Google developed their own support and built that support into the native app.
Verizon had their own RCS support via a proprietary carrier-specific app that never worked with anyone outside Verizon as far as I remember, and they dropped it in favor of Google’s option as soon as that was available. Samsung had their own RCS support in their proprietary Messaging app, also dropped because Google provides the same support on all of their products and Samsung doesn’t have to do anything or support it in any way. Google now provides an option for all Android devices specifically because almost no one was adding support on their own.
Anyone can, no one else will, because they have no reason to. The average user doesn’t care whether it’s Google, their carrier, or the manufacturer providing support for sending high quality photos to their friend’s phone number as long as it works.