Not just Google is the problem, the entire industry is the problem. Almost all of the cell-based standards are locked away and purely depend on the operators, major infrastructure companies like Motorola, Ericsson and Huawei and modem implementors like Qualcomm, Apple or Broadcom.

Implementing them independently is extremely difficult and even if you manage to do it you cannot have them commercially available due to radio regulation and patents. Even academic research can only be done with collaboration of those huge companies.

It is impossible to make a phone that is LTE capable completely independently (or even without nation state support). You cannot implement VoLTE or RCS without support from the carriers. They all have their own proprietary protocol on top of the standards.

Google has basically infinite money and their own patents and industry relationships and government support so they can figure out RCS. An indie company, even with infinitely motivated engineers and good funding do not have any of it.