I think the failure rate is so high because many never really try to make it an honest business. I can't tell you how many people I run into that state they tried and failed, but when we go deeper and talk about marketing, start up funding, research, target markets, branding, etc, I get a blank stare. Most bought a camera, couple of lenses, printed some business cards, and setup a portfolio and website, and limited marketing. Very few did any real work to make it successful. For the most part, it was a hobby they were trying to make money on the side, and never approached it as a real business.
Of the half dozen or so that actually approached it as a business, I know two that are still in business and seem to be doing well. I don't pry into their financials, but they are growing, have studios, and been at it for quite a while. Not sure about the others, as we've lost touch over time.
I gave up a cushy corporate job, and have no regrets. I'd do it again in a heartbeat, but sooner than I had originally knowing what I know now.