The software is free, but no dev works for free.

It's possible to engineer software well and still earn a living.

That said, engineering software poorly is often a choice, usually made by people who are poor engineers. In some cases, and I suspect this may be the case for Nabu Casa Inc., the people are such poor engineers that they aren't even aware that their software is poorly engineered. Many technology companies are better at business than they are engineering.

Edit: actually no, I don't think Nabu Casa Inc. are unaware of their poor engineering, I think they just don't care. They're far more concerned with maintaining their company's profits.