Because in a cross examination, you're supposed to ask very narrow closed questions (yes/no answers only) in a series, so that you get the evidence out in the way you want the decisionmaker to hear it. Ideally, the witness isn't supposed to catch on to where you're going so that they don't try to weasel out of answering them with "weeeelll.. not really because..".
But you don't ask "the last question", which is the one that sums up the point you were trying to make, because then the witness sees how you've shown them to be full of shit, and they'll spend 10 minutes weaseling out of everything you just established. It's SO TEMPTING to ask it directly, because you really want to hit the point home, but it's often too risky because it can backfire by breaking up your flow -- you often have dozens of lines of questioning, and there's a "last question" to each of them.
What you're supposed to do is explain "the last question" in your final submissions, using the transcript from your cross as the proof the statement is true.
But you don't ask "the last question", which is the one that sums up the point you were trying to make, because then the witness sees how you've shown them to be full of shit, and they'll spend 10 minutes weaseling out of everything you just established. It's SO TEMPTING to ask it directly, because you really want to hit the point home, but it's often too risky because it can backfire by breaking up your flow -- you often have dozens of lines of questioning, and there's a "last question" to each of them.
What you're supposed to do is explain "the last question" in your final submissions, using the transcript from your cross as the proof the statement is true.