It's almost always because it's a labor of love and isn't worth the money.
Richard Douglass created Ballroom Dancing competition judging software because, as a competitor, he was wasting vast amounts of time with crappy judging and software (especially because a lot of software wouldn't deal well with garbage network connections). https://www.douglassassociates.com/
It has roughly 300 uses per year. It charges roughly $1000 per use. That's about $300K per year for taking the support calls, managing the credit card bridge, and updating any features due to the OS makers breaking shit.
They have a plan to release the code when he passes. However, that probably isn't enough. It's likely nobody has the programming AND ballroom dance competition experience necessary to keep it going.