That is a real concern, but I don’t for a minute believe that it’s Google’s only motivation. This is also securing a revenue stream and making it harder for others to compete.
Full disclosure, I am an iPhone user in part because I personally like living in the walled garden. But I also acknowledge that it has its downsides. I have a separate Android device just for language learning because the open source language learning app ecosystem is basically nonexistent on Apple’s locked-down platform. I’m not thrilled about the possibility of that ecosystem withering and dying on Android, too.