Why Apple Put an Aperture in the iPhone 18 Pro

Apple announced the iPhone 18 Pro, and the headline camera feature this year is a physical variable aperture on the main camera.  I have been shooting professionally for 20 years, and I sat through that entire section of the keynote thinking the same thing over and over: this does not make any sense. Why would anyone want or need a variable aperture on a phone? So I went and did a pile of research, and I think I finally know why it is there. It has almost nothing to do with the reason