Because businesses always support their software better than individuals?
I wonder why they all start their own projects instead of putting their heads together. They could achieve so much more and make a bit more money on the side, while each of them would have to spend less time on it. It would also attract risk-averse companies.
I was amazed to find that a) nobody maintained the project after I left, there were only two minor fixes because their house was on fire, and b) I really took the time to write almost complete documentation on all the important topics, which helped me get back on track faster.
You are absolutely right, and I have experienced this most of the time. The problem is that it is an uphill battle to explain to most stakeholders why you are "wasting" so much time on non-customer facing documentation.
It is hard enough to convince even technical stakeholders (e.g. product owners) to write automated tests.
While at the time I mostly think it's bad, later on it forces them to pay me twice as much, so I guess it's not as bad as I always think in those moments :D