Because most Americans believe it both is real and is a problem and Liberals reliably will react one of two ways? One, they will deny it exists at all. Two, despite denying it exists will argue its a good thing.
Ben Burgis, hardly a Right-Winger, even has a book coming out called
Canceling Comedians While the World Burns. So this is something Leftists are also critical of. Though Liberals obviously are more likely to view it with a positive light. But, it is considered to be a thing by Americans, and widely disliked and viewed negatively. The chief reason, taken from a
Bloomberg piece is that:
The findings are more consistent with what the critics of cancel culture are saying. The line of unacceptability is constantly, rapidly and unpredictably shifting; sanctions for crossing it are applied arbitrarily but sometimes harshly.
That article has further links to further information.
Trumps strategy makes sense because it patently exists and Trump can count on his opposition to either deny it exists which makes Liberals look daft and dishonest, OR more ghoulishly, will argue its a good thing, which no normal person likes the idea of living under a highly punitive ever shifting and largely unknowable set of rules in which anything said or done at any point in your life can be seen as a pretext try at least to make it impossible for one to live in society, I guess normal people don't like the idea of having to follow an ever shifting code of conduct in which the punishments can be as extreme as "You might as well kill yourself".
Trump is capitalizing on the fact that Liberals WILL react in only two ways, either denial, or say its a good thing, or both. Which makes Liberals look sinister and menacing. It's easy to run on an issue by saying you share an opinion the majority also shares.