IF I understand things correctly each project is usually a different corporation. Different investors for different projects, one failed project won't impact other projects, a failure doesn't impact anyone personally, etc. Basically look up all the reasons you want an S-Corp or LLC rather than a sole proprietorship for your own business. I think his bankruptcies are several of these projects failing. If only several projects failed out of dozens he's doing pretty well.
However, if trump had merely stuck his inheritance money in a market ETF and then fucked off to play golf for the last 25-30 years, he be 3x-5x as wealthy as he is now. (the variance depending on just how much you believe he's actually worth now.)
25 years of 'projects', wheeling and dealing, real estate, steaks, wines, universities, casinos.
My own simple investments have done better than Trump over the last 2-3 decades.
The only difference between people like me and Trump is that Trump started out with a couple hundred million, and I didn't, so even earning wildly sub-par returns he's STILL a billionaire, and I'm not.
Really, how much success do you want to attribute to a businessman who trailed the market by THAT much?