The only difference between the guy who owns a successful Veterinary practice and the guy working as an underpaid veterinarian is that one of them went out and leased some office space.
I understand the point you're attempting to make but the guy who owns the <type of business> has done much, much more than simply lease an office.
Many business founders put their life savings on the line. Those who don't have that luxury ramp up thousands of dollars of personal debt.
On top of that they work every waking hour. Time is a precious commodity and cannot be replaced, so risking so much of it to enjoy the slim chance of being a successful business owner is not something most people care to risk.
I didn't have to buy an MRI machine to start doing my thing. I just had to register a domain name and sign up for a Stripe account.
Incidentally, there's a lot of room to build a successful software business with an effort between zero and "work every waking hour"/"put [your] life savings on the line". I built the products I live off in the downtime between contract gigs, when the surf wasn't working and conditions weren't right for climbing. With two digit hosting expenses for the first several years.
Definitely don't let fears like the ones you expressed above stop you from doing it.
You may be the best engineer in the world, if you don't know how to find customers and get paid, make good investments, and do all the bookkeeping, or, alternatively, hire the right people to do it for you and manage them, then your business will fail.
However, if the only thing you know is how to do business, then all you need to do is hire a competent engineer and you will succeed.
If you think some of the equipment is 100k, x-ray 30k per plate. You also need a territory before you start. It is too easy for bigger practices to starve you out to just pile in 250k and hope for the best.
You have to join a small practice, crawl up through the ranks, getting paid next to nothing, somehow kill your colleagues before they make partner and then you might be in a position to jump ship stealing customers as you go or organize a coup take over the practice by joining with another bigger practice nearby and buying out the seniors.
If you had said lawyer now... I don't know maybe - but I got your american dream point.
His motivation for doing so was a conversation with his previous boss that included the quote "because I went out and got a lease on a building".