Because she doesn't want to answer the question. She didn't want to answer it later, either, when she continued to insist that she bore no responsibility at all for Trump being totally unfettered now. Her vote against impeaching Trump, she told reporters, "wasn't based on predicting his future behavior." Which is a hell of a cop-out for the person who once said impeaching him would be enough to make him curb his future behavior.
Collins is completely abdicating responsibility for both her past and her future failures to do her goddamned most essential job of being a check on the president. What she does think is her job is not obvious (besides granting defense contracts to companies that in turn contribute tens of thousands of dollars to her reelection campaign).
MR: In light of the president's actions, do you think there's any lessons he heard from being impeached?
SC: I don't know what actions you're referring to. I've made very clear that I don't think anyone should be retaliated against. That has nothing to do with the basis by which I voted to acquit the president, as I made very clear to you, Manu, on numerous occasions because his conduct, while wrong, did not meet the high bar established in the constitution for the immediate ouster of a duly elected president. And that was the rationale for my vote to acquit him. That is the reason why….
MR: Do you think he learned any lessons?
SC: … In all the years that … since George Washington was inaugurated as our first president that we have never removed a duly elected president from office. It's because the conduct alleged should be so dangerous to our country and so egregious and proven by the House managers that the person should not remain in office one moment more. That was the standard established by the House managers. It was the standard that I used in acquitting President Clinton and that's the reason for my vote and I don't know why you're equating the two.
MR: Well you said the president learned his lesson. Do you think he learned any lessons?
[Collins’ office door slams shut.]