Hahaha great question. It's funny how I thought it was a silly question when asked the other way. In a way, my response is the same for both phones: 'The main thing stopping me is that I am not considering switching'.

That said, I carried both for years, so I can probably provide some insight. I switched from Windows Mobile to iOS in 2008. I had one phone until 2012. My "main" phone was iOS from 2008-2017. The biggest factor was (and still is somewhat) who had the best camera. Pixel 1 had a better camera, so I switched to Android as my main in 2017. These days, both have great cameras and it wouldn't be a reason to switch.

My current job doesn't need me to have two phones, but I still carry an iPad mini, so I remain in both ecosystems.

I prefer Android on my phone for lots of little reasons, but they all basically boil down to the same thing: Android lets me do what I want with my phone.

It's difficult to explain if you haven't been an Android user. If you don't know what a launcher is, it's the interface between you and your apps. I've never much liked Google's launcher. I don't like Google's keyboard, so I use my own. I like to change the default number of rows/columns of my app icons. I like switching between two bottom-row docks. Then there's stuff like default apps, and way better widgets, of course. Plus I can arrange my apps how I like.

Now - if you are on iOS and have never had this stuff, you won't miss it. If you want your phone to "just work" and never think about personalizing it, you have no reason to even value the personalisation that Android offers. But, if you've gotten used to your personal phone layout, being forced into the Apple way is restrictive.