I think there are often several candidates in the primary election for any given office (not just president) that would like to, but it only takes one stalking

I think there are often several candidates in the primary election for any given office (not just president) that would like to, but it only takes one stalking horse funded by the rich in either party to ad-bomb the election, fragment the vote between the better alternatives, and rake in a plurality of the votes for the win. There are probably several ways around that, but why change it, since the system is "working"?