Those of us who work or dabble in photography are aware of a diabolical disease that affects us - G.A.S., also know as Gear Acquirement Syndrome, also known as leaving your grandkids nothing.
I was a working pro photographer for over fifty years, I used needing to be prepared for any contingency as the reason to maintain an arsenal of lenses and cameras in different formats, not to mention a closet full of lighting gear. I retired from assignment work about 10 years ago, so why am I still buying gear? In part for the same reason, contingencies.
Now many of us, especially of the very old school, believe one or three lenses should be all you need. After all, Henri Cartier-Bresson worked with a Leica with a 50mm lens for many years and became a legend. I recall early on I worked with a Minolta SRT101 and 3 lenses, 35mm, 50mm and 135mm. My shoulders long for those days.
I think I took on paid/pro photography work in part so that I could justify buying the gear I wanted. Maybe not the best business model/plan, but I do enjoy nice gear that makes me happy to use, for the benefit of my clients.
The amount of gear I've collected is also a lot of 'just in case' contingency reasoning. Redundancy is also important. I'm a bit behind the curve with lighting equipment - it's good stuff, just a bit on the old side now. The problem is it's now easy to find it very inexpensively and difficult to resist buying more 'just in case' and as redundancy for when/if existing units go down (and also less expensive to replace those rather than servicing them).
Maybe not the best business model/plan, but I do enjoy nice gear that makes me happy to use, for the benefit of my clients.