Explained simply, the Mango Menace cares only about one person in his life: himself, all the time. No-one comes ahead of him, not even family. He will throw anyone under the bus without the slightest compunction of guilt if it furthers his own immediate ends - whole businesses, associates, contractors, employees, family members...all are Trump-expendable.
So Gorka being tossed is easily explained. He may have shared similar views with Trump and been a Breitbart good-guy and a blatant Nazi equivalent. But throw shade on Donny or cause him any personal itching and there won't even be a gangplank. Straight over the side you go, no notice, no recourse, no compensation.