Google’s the main backer but it’s technically an open standard. Apple is implementing support in iOS 18 too, reluctantly. Google also has non-standard extensions on top of it like e2e encryption. I wish they would standardize it but that’s a pretty important feature and maybe it’s ok that they brought it out before it could become standard.
The part you’re missing is that while C++ does have newer safer ways of doing memory management, all the old ways are still present, in wide use, and are easier. Basically, C++ makes it easy to do the wrong thing and hard to do the right thing, and most codebases are built around the wrong things. It’s often easier to just rewrite it in rust than it is to refactor an existing code base, so if you’re going to expend that effort why not do it in a language that has stronger safety guarantees, a better dependency and build management system, and a growing community?