Google didn't create RCS. The idea was floated in 2008 and in 2009 the GSM association (Non-profit, representing 700+ mobile carriers across the world) began directing the project. Since then 47 mobile network operators, 11 equipment manufacturers, and 2 operating system companies (Google & Microsoft) have pledged their support for RCS.

In fact, Google only started implementing RCS in 2019 whereas Samsung has been releasing phones since 2012 with RCS. Now RCS is actively used by over 88 operators in 59 countries with almost 400,000,000 daily users.

tl;dr - Apple not using RCS is Apple's problem when the rest of the world does.