It's the philosophy of Arch to stick to vanilla as much as possible and keep things simple. It's a rolling distro too with no fixed release cycles. When you upgrade fedora, ubuntu, etc. they perform various scripts to migrate existing configuration. In Arch, it just simply installs the vanilla packages whenever you tell pacman to update. Very rarely there is some breaking change, maybe once or twice a year, that requires manual intervention. Yeah they could automate it all but such stuff takes effort and breaks in other ways.