I don't buy that. That is what the media wants you to believe that it's a petty personal vendetta. Think about the conflict of interest there from the media.
Trump attacks the Washington Post and complains about Amazon pretty much in the same breath. It is easy to draw one’s own conclusion that he is attempting to ‘punch back’, as his wife described his tendency.
I don't think Trump thinks attacking back is petty. He pretty reliably attacks anyone who attacks him.
OK, so why do you believe Trump is picking this particular fight with Amazon?
If I had to speculate because Amazon is hurting and putting lots of small American businesses out of business. Many workers and owners are part of his base.
Why isn't Walmart drawing his ire as well then?
Because Walmart doesn’t have a newspaper that’s been critical of him.