All of Google's services are also on iOS, often the apps work better than on Android. There is no barrier to switching.
I'm not saying is impossible or something, but it's just way more effort than it was worth to me. E.g. so many iOS apps by default are set to use iCloud. All of my photos for years were in Google Photos. There is a Google Photos app for iOS, but it is in no way as seamless an experience as on a Pixel (e.g. camera integration). And I think a lot of people would say that if you get an iPhone but specifically avoid Apple's services like iCloud for photos so you can stay on Google's services, that defeats a huge part of the value of being on the iOS ecosystem in the first place.