The answer is actually much simpler.
And I say this as a Cruz supporter
Cruz sounds like he’s getting ready to fight a boxing match with Marquess of Queensberry Rules.
Trump sounds like he’s getting ready to fight a no-holds barred gutter brawl where the last man standing is the winner.
And the Republican electorate wants a brawl and not a boxing match.
If Cruz wants to win he needs to sound more like a fighter and less like a lawyer.