Opportunity cost and time value of money. In general, if person A puts $5K a year into a 401k between ages 25-35 and then stops, while person B puts in $5K a year between ages 35-65, at age 65 person A will have a larger retirement balance despite having put in only 1/3 as much principal. This generalizes to the rest of your net worth (salary+stock) as well.
If you win the lottery and manage to have significant equity in a startup worth millions, congratulations. If not, you're faced with the prospect of being older and having minimal (or at least far fewer) assets. This is a big problem if you want to raise a family or even if you want to advance your status in life.
The economics of software are simply different. Someone good enough to start a business that brings in $10-20K MRR and barely survive is almost certainly good enough to get hired and paid $200K+ by any number of companies. If you're not going big or going home, it doesn't make sense to do a software startup these days.
Even in other industries, starting and running your own business is a LOT of work. If your goal isn't to (try to) get rich, you can almost always make more money climbing some corporate ladder for a lot fewer hours.
