Unfortunately this is not limited to photographers.
In my contracting business, I keep coming across the wanna-be contractors who figure I (and other contractors who have been in business for a while) are making a killing, and they want some of the action. Some of them were my former employees that I trained. What they don't realize is that there much more to the job than buying product and installing it. For some reason, they end up lasting a year or two, and then they're working for someone else again, poorer, and usually not much wiser.
One of my acquaintances loves baking. So she set herself up as a professional baker. Uh-oh. There are various laws covering the operation of a food-producing facility. There are permits and certifications. There is commitments for rent, utilities, and professional services. Then there's the challenge of finding enough customers to cover the monthly overhead. All of the sudden, it's not as much fun any more.
I know another person who believes her calling in life is to be a motivational speaker. She's got energy all right, and can talk. But there's this little issue of having to find customers, arrange for venues, handle the logistics, cover the insurance, business taxes, and various permits... and she's struggling, because she's got the 20% (the speaking part) more or less covered, but the rest of the stuff is just a lot of headache and drag.
I have seen successful small businesses, but they tend to be partnerships of like-minded people who divvy up the hard work and each is good at what they do. Someone has to handle production. Someone else is dealing with marketing. Someone is looking after administration, cashflow, and making sure all the regulatory stuff is handled on time. Someone has to do the sales. And if there are employees, well that's another can of worms.
It ain't easy.