> I would guess there are many cases of solo founders shutting down their business other than founder death...

Sure, but it really only makes sense to consider cases where:

A) The business has paying customers

B) It's very important to the customers that this product remain available

C) The founder is unwilling to give or license the source code to those customers

In practice, all three of these factors being present is uncommon. Usually if the product is actually important to a customer, they just pay to acquire the assets. And there is usually no reason for a solo founder not to take that deal if the alternative is just shutting down the business.

For a venture backed business, maybe the lawyers decide there is too much legal risk or whatever. But for an indie hacker, that doesn't happen.

We hear stories all the time of folks getting burned when venture backed startups shut down without giving people any time to switch to another product, or sometimes even to expert their data. When is the last time you heard about this happening from the paying customers of a solo founder? Literally never.

You’re comparing apples to calculators. Solo founders go out of business literally all the time, every day. I’ve definitely heard of solo devs canceling. It’s also like the entire reputation of the KickStarter experience, pay a solo dev to do something, get nothing in return aside from a bunch of hopeful emails followed by silence or a sorry.

Software created by solo devs is used by many times fewer people, therefore it’s zero surprise that the total number of displaced customers is lower. You need to calculate the percentages, not hold up anecdotes of not having any rumors.

I don’t see how (C) can reasonably factor into any statistics. I’d love to hear how often you think this matters, but I’m extremely skeptical that shutting down a solo business and giving source to customers has happened enough times to even talk about relative to the number of times that hasn’t happened. I’d like to hear about when giving source to paying customers is even helpful. Depends highly on what kind of software we’re talking about, and depends highly on what kind of customers, but assuming that paying customers can generally do anything with source code seems like a really, really big assumption.