Because who has power already and knows how to use it without spending money?
I think it’s more a case of Trump knowing how to use the pulpit, and Cruz, for whatever reason, can’t or doesn’t.
Take illegals, for example.
Trump isn’t saying anything much different than Cruz, but look how much traction his style of presentation got him. He’s done more in 3 weeks than Cruz has been able to do in 3 years.
That’s why Cruz would, or could, learn a lot as VP under trump.