I created CalendarBudget years ago to solve a personal problem - every budgeting/financial planning app out there was terrible and didn't allow me to plan my future very effectively. I created CalendarBudget to "scratch my own itch" as it were, and it continues to make thousands of people happy today. For a while, I used to charge for it and tried to have a go at working on it full-time. It was great fun and I loved creating such useful software for people, but in the end, it didn't generate enough money to be a full-time job, at least not then.
Since then, I've been running CalendarBudget for free. I make no revenue from it whatsoever. I am a Christian and part of my beliefs include giving back to the community/world and serving selflessly. Hopefully I've been able to do that. I plan to continue doing that through CalendarBudget.
I've hummed and hawed about charging for CalendarBudet again in order to justify spending more time on it for more features that have long been requested/planned (such as a mobile app, revamping the category sidebar, etc) or just answering support questions. I've considered running ads, creating a subscription, asking for donations, charging for support, or finding some other revenue stream. But, every time I do that I keep thinking that the people who need this the most are the most unlikely/unable to be able to pay even a small amount... and perhaps the most vulnerable to product advertising for things they don't really need.
So, in order to continue serving the community/world, I've kept it cost-free and ad-free.