Because many of Trump's base are low-educated rural people who see the American jobs being generated by the best foreign entrepreneurs as requiring higher education and skills than they possess.
And while it's true that the white rural poor vote Republican, as a political force they aren't that potent. It's unfortunately, because their interests often get steamrolled by more corporate-oriented Republicans. Democrats throw their arms up and say "Stop voting against your interests!" but neither party has any coherent vision for rural America. Republicans see them purely as culture voters, and Democrats are focused on giving them the same complicated means-tested benefits as everyone else.