Multiple people have said "the ecosystem", and I'm just going to say the same. It's not just a question of iPhone being better or worse than Pixel. It's Mac, iPhone, iPad, Watch, AppleTV, AirPods, CarPlay, all seamlessly integrated and all receiving support and upgrades in perfect synchronicity. Every device receives upgrades, generally on the same day, to support new features across the entire ecosystem. And if I ever buy a Vision, I already know it's going to be seamlessly integrated with every other device. If Apple comes out with some new CarPlay that I get in my next car, I already know it will be cleverly integrated with my Watch and iPhone in ways I can't even anticipate.
The integration continues to get better, and more seamless with every update. Media, calendars, passwords, email, contacts, browsing history, browser bookmarks, and messaging are all automatically synced. If I buy a new devices, I just log it into iCloud, and everything automagically syncs up. I don't have to spend the afternoon configuring individual integrations with plugins and apps. You basically just log in to iCloud and you're done.
A new feature is coming out in the next OS that allows you to control your iPhone from your Mac. I can already control my iPad from my Mac with universal control.
Introducing a non Apple device into the matrix is just going to break the seamlessness of the ecosystem. You can point out a single feature you like from the Pixel, but however nice it is, it isn't going to come close being compelling enough to convince me to break with the ecosystem. The ecosystem is just too good.