It’s almost like the iPhone is a fetish or totem that grants access to iMessage (although you can message from macos or iCloud.com impractically).
It’s quite strange how this is a very simple, solved, problem for iPhone for many years. Google can fix it by literally cloning iMessage and arguing with carriers. They don’t. I suspect it’s because they want to be the only one with access to the cleartext and they aren’t willing to make a consumer-focused decision to keep all messages ciphertext.
So “most of the planet” has to suffer Google’s anti-consumer decision.
It’s like buying a diesel vehicle and then complaining that the hybrid systems suck for them. Don’t buy a diesel if you want hybrid engines. Or work with the manufacturer to change their incentive model.
But google is an ad company and is unlikely to make products where it is hard to sell ads.