Google seems to be making some major changes to the way that they are approaching the mobile space, mostly centered around their Assistant AI platform and mobile apps and services. One of the more stark and shocking proofs of this new mentality is the fact that Assistant will soon be available on iOS. Google Home, meanwhile, is getting more and more features by the day, while Google Photos, YouTube, and Google Play Music, among others, are gaining wider and wider user bases across various ecosystems. Some of these are getting new features announced for them at Google I/O that are completely ecosystem agnostic, such as Google Photos offering to let users share photos or order physical prints and albums.
Google is taking an approach similar to Amazon's Alexa with their Assistant AI, spreading it from platform to platform and giving it the ability to grow outside of the Android ecosystem. Rather than use it as a killer app of sorts for Android and Google Home, they want to bring it to everybody, and have a shot at potential indirect revenue gains from all platforms. Given that most of Google's apps are already available on iOS and they make just as much money from an iOS user doing a search or watching a YouTube ad as they would a web user or Android user, this makes perfect sense.
Google Assistant is far from the company's first product to adapt to the wiles of a marketplace based mostly on free services that are freely accessible; they've technically been in that game since their founding, back when their search engine could run in any browser and serve ads to anybody. Assistant held sway as a real competitor to other AI-based voice assistants out there and stood a good chance of helping to gravitate users toward Android and Google Home, where the company would have more chances to generate revenue from them. Instead, Google is bringing Assistant to other platforms, just like any of their other multi-platform efforts, in the hopes that users of that platform will prefer it over the comparable solution that came with their platform. From there, Assistant's tendency to link to and use Google products and services can help to bring in the revenue from users of other platforms who may otherwise have not used those services.