The first reason is that parties have been regulated and are what make our parliamentary system work. They are heavily regulated and are provided for in the legislation.
My idea is that you list the parties—maybe in alphabetical order; it doesn't matter—and then an individual can choose a party. The ballot would have the name of the candidate and the party. Then that would just rotate through each ballot. It gets a different one at the top, and it rotates. It's the first thing you see on the ballot. You can ignore that. You might say, “I don't want to vote for any of the parties. I hate political parties. I'm going down to the list of independents.”