I guess it's part of the trend now. Some time ago both Google and Apple rolled out very flat UIs -- Apple in iOS 7 and Google with Material Design in Android 5, and both where mostly flat. I don't know, maybe they were influenced by Microsoft's Flat UI that ultimately went nowhere. Yet, over time, Google began introducing more and more meaty designs with more aggressive rounded corners, eventually ending up doing everything very curvy. Maybe folks at Apple looked at that and wanted some of those curves, too. So previously the trend was to flatten everything, now the trend is the reverse of the previous.