Because this looks really fucking bad. Like even by Trump standards. They know that their best hope is turning this into another heated alternative facts culture war issue.
They do this not because they think it will actually change minds, but because it makes talking about "the most recent crazy thing Trump did" a "political statement" which means people can't bring it up at work or around certain family, etc. If they turn it into a political third rail it prevents people from talking about it.