I believe Google (maker of Android OS) and the big telcos that use android on their phones want to be able to have interoperability with imessage so users of imessage and android messenger can seamlessly text one another but they cannot because Apple will not allow it. If Android and iphones users want to seamlessly text one another both need to install another text app that works across both platforms.
I believe there are settings that one can change in Android to get it to work properly with imessage but that defeats the whole issue of having both phones OS seamlessly working together.
Users of android phones should not have to mess around with having to install 3rd party apps or make phone setting changes to get it to work with imessage but Apple's refusal to allow both messaging platforms to work together is what is causing the problem.
If the telcos really wanted this then they would have just adopted RCS, it was already set and ready to go but because they could not figure out how to make revenue off of it they let it die. If the telcos adopted it then Apple would have no choice but to support it. Note we're not talking about the same RCS as Google's proprietary fork. All of this squawking and you know who we do NOT hear complaining? Telcos. The blame, IMO, falls back on telcos and even more specifically on the regulatory bodies which didn't force them into adopting a new and better standard.