I have been a political junkie since 1972. So I know exactly how primaries work. The best way to win a primary is to divide and conquer.
For example, in 2012, Romney was the most liberal candidate. While Santorum & Newt were more conservative than Romney.
So what happened? Romney had a hard time crossing 30% in most initial primaries.
Near the end, only 3 candidates remained. Romney did not have to split liberal republican voters with anyone. But Newt & Ricky kept dividing the more conservative voters, and cleared the path for Romney.
If you really want Cruz to win, encourage as many liberal republicans to enter the primaries as possible. Let them divide votes this time. Since Trump is a liberal, and JEB is a liberal, and Christy is a liberal, the smart strategy is to encourage them to stay in the race.
The ultimate goal is for a conservative like Cruz to win nomination. Why hurt Cruz by killing off candidacies of liberal Trump & Christy? They are useful to split votes with JEB, who has enough money so he is unlikely to drop out.
If you were as knowledgeable as you claim to be you would know how damaging a joke like Trump is to the Republican Party.