Because of many reasons that are faulty thinking. For example: He's racist, Not one instance was he found guilty. They like to use the time he had to go to court for being accused of being racist for a housing development that didn't let blacks in, but that wasn't the case, it was because most people in that area couldn't afford it that was black. And maybe the people inside was racist in a way but NOT Trump. They may have turned down people of color that looked like they couldn't afford it. That is wrong but many places do this now, not just for blacks but for whites, mexicans anybody they don't like that has a poor attitude.
He settled by paying for signs in that area that was "racist" saying blacks was invited, he was forced to do that because of the settlement.
Then they accuse him of being racist because he wants a secure border or saying many people are coming in illegally that have been raped or rape others. Which is true. Among other severe crimes.