Main reason is that Android devices get outdated much faster, because developers of Android OS can not provide proper support for every single device which runs it, thus when it updates - older ones quickly start lagging/bugging/etc. Also Android OS itself is still bad compared to iOS.
If you have money = you pay for comfort, that's how it works.
Go for iPhone 8, it's best money/value devices at this moment. Or wait September when new iPhone will be released, and get X.