I haven't felt a need to root a phone in years. These days you will get a usable UI and UX with basically all major brands and adblock can be done without root, so it's just not worth the hassle trying to hide the fact that you're rooted from banking apps etc. At least as far as I'm concerned, I'm sure that some people still see a benefit in rooting.
Edit: I actually just thought of a reason: updates once the phone is past its official support window but otherwise still functional (though you don't technically need root for that, just an unlocked bootloader, the new ROM doesn't need to be rooted either strictly speaking). I'd just buy a new phone, but that really just means I'm a part of the e-waste problem.