The Republicans need to consolidate their support behind Trump and fully promote him winning back the White House in 2017.
Once the democRATS pick Hillary, the entire party will back her in the November election. Once the GOP voters pick Trump, some conservatives will go home, complaining that their guy didn't win the primary. They won't vote and Hillary will take it in a cakewalk.
Because what they really care about is globalism, controlled by, and for the benefit of, the multi-billionaires.
With those goals, 1) globalist candidate (Democrat) is preferable to 2) America first and last candidate (Republican). They'd prefer it to be globalist candidate (Republican) though, since they like to alternate the party which occupies the White House. It helps to keep the population under control when the voters think it will make a difference when the candidate from THEIR party gets elected. Make them think if they "throw the rascals out" that things will be all better.