"We're funded by the goodness of a team of volunteers" is a great answer.
Audacity: Free until 2021 when they were bought and introduced telemetry.
Streamlabs: Open-source but tried to monetise and attack the OBS brand
Bitwarden forks: Various forks of open-source code that included monetisation
OpenOffice: Great desktop apps until bought by Oracle
CCleaner: "free" software that contained trojens.
HoverZoom: Chrome plugin sold by original dev, new update included spyware and ads.
As I said, I don't mind if the answer is "we are volunteers who love this", but I do ask that formal webpage presenting a product, that even has an FAQ page, explains it's funding model. Their github (https://github.com/CelestiaProject/Celestia) is much better at this.
Being offended so quickly, I'm tempted to ask if you're new to the internet ))
openAI: Microsoft has invested US$13 billion in OpenAI, and is entitled to 49% of OpenAI Global, LLC's profits, capped at an estimated 10x their investment.