Most non-software businesses require a much higher upfront investment. With hardware, retail, restaurants or other brick-and-mortar businesses you've got one chance more or less. If you fail in these types of businesses a large amount of capital will be lost (quite likely including your personal savings).
With software businesses you can most of the times just start over. Plus, there always is the opportunity to do consulting if your original plan doesn't work out. As a developer you have a few fallback options whereas in other industries it's mostly all or nothing. While this is an advantage for developers it can also be detrimental. Most developers want to start a company but how many actually do and how many of those persevere when problems come up? With a non-software business you can't bottle out as easily once you've started.