It's not that simple. Google has quasi-monopolized RCS as a way to fix their haphazard mobile messaging offering. To put weight behind their argument, Jibe was

It's not that simple. Google has quasi-monopolized RCS as a way to fix their haphazard mobile messaging offering. To put weight behind their argument, Jibe was rolled out almost worldwide and enabled for every Android phone running Google Messages. "Look, we have one billion active users". Once Apple finally caved in, it became harder to hide a proprietary end-to-end solution behind a standard. While MNOs are still using Jibe, they have to support spec compliant IMS provisioning that allows the iOS client to register to Jibe. Some carriers have started migrating Android users to their new registration workflows and associated terms and conditions. To my knowledge, Google provides P2P messaging for free but there must be conditions. MNOs need to agree on revenue share for A2P messaging, and while I don't know if iOS support will become mandatory, this would make sense from Google's point of view. This is textbook drug dealer model and it makes sense that a few MNOs won't play along, especially in countries where WhatsApp dominates the market anyway.