Basically the better display for the XS Max and the better camera. The additional screen estate is always welcome, and Smart HDR seems to make the photos pop out more (based on what I observe from my friends; I am currently using a 8+).
Headphone jacks stopped mattering to me after I got the AirPods. I am nowhere close to using up the 256 gb of storage on my 8+ or iPad Pro. I don't use a case or screen protector with my devices, and have been charging them off the same USB hub that I bought a couple of years back, so the lack of a fast charger or accessories doesn't bother me. Heck, my headphone jack adaptor is still untouched in the original packaging.
As I said before, it's all about the ecosystem and the integrated experience, and Samsung can only go so far by pumping hardware specs.
With iOS, I get message forwarding (allowing me to send and receive SMSes on my iPad and Mac), universal clipboard, airdrop, handoff etc. I am a happy user of apps such as bear, things, overcast, fantastical, Tweetbot and Apollo, apps which I would have to give up moving to Android. I am also guaranteed 5 years of software updates.
They may not matter to you, but I find them useful, and in the same vein, many of the benefits of using an android phone don't really appeal to me either. I guess that's why each of us are using the respective devices that we are, but I find that more isn't always better, especially when it doesn't give me more of what I want.