This is all really the fault of The Apprentice, who made him seem as if he were some kind of business genius.

Trump was decent at making himself seem like he was a good businessman. But, all his self-promotion had to compete with all his failures. Eventually he would have run out of money to self-promote.

Then the people behind The Apprentice came along and did everything in their power to make him seem like he was the best businessman in the world, and idiots bought it. People watched a fictional reality TV show where contestants had to do silly "businessey" things, and somehow they concluded that the guy at the boardroom table set was actually good at business, rather than competent at acting.

This barely competent idiot who had inherited / stolen half a billion from his father and was slowly burning through it with his various failures had worked his entire life to try to create a myth that he was a genius businessman. That attempt had almost failed as he ran out of money. Then the guy who made Survivor came along and made his dreams come true. Finally, he was on TV all the time playing the character of a shrewd businessman, and somehow getting paid for it. This show lasted a decade, and by the end of it, idiots were convinced that Trump was a business genius, and the rest is history.

Oh, and incidentally, Mark Burnett, the guy who created The Apprentice, is now "United States Special Envoy for the United Kingdom", appointed on Trump's inauguration day in 2025.