While working on my blog, I felt like reading the 6-year-old post "5 reasons why I write free software" http://guillaume.baierouge.fr/2014/10/02/5-reasons-why-i-write-free-software/ Apart from some broken links that needed fixing, I think all points are still valid today.
I initially wrote this because at the time, a few Sozi users sometimes behaved like "customers", as if Sozi was a commercial "product", which implied that I had an obligation to develop features on demand, help users, etc.