Because OWN THE LIBS
If Stalin came back from the dead and signed up as a GOP candidate, he'd get the overwhelming majority of the party voting for him based solely on him being on the GOP ticket and opposed to whoever was the DEM candidate. Simple as.
And if you're wondering how he even got this far, it's because loud bombastic people get more attention than sane people. People voting in primaries see "Joe Shcmoe" and "Hulk Hogan" on the ballot, guess which one they're going to vote for without spending one second looking into their positions?