IMHO it’s two things.

First, the touch to screen response time.
How long it takes from the time your finger touches the screen to the corresponding action being seen.
Where talking about 50-60ms. It’s seems counterintuitive, but it makes a difference.
All iPhones rank really high in this. In fact most older iPhones are better than this generation’s (as these have some issues).

This is the result of two factors: the better screens (not so much at the pricier devices, but for mid tier it’s a crazy difference) and also the integrated development of the whole device.

The second is thing is the tools Apple provides for developers.
Android moved a ahead a lot in this matter, but it’s still tracking.
I’ll spare most of the details, but the apps developed for Android aren’t optimized to run in the processor directly, they use an intermediate state. iOS apps are compiled to be fully native for the processors they’re ran on.
This being better performance, hence faster response times, better animations, …

I’m Tim Cook.

You can now have the M3 8 GB 512GB for $1199.
The 16GB still costs $1799.

Have a good day