It is because you are passion driven. It's normal and you should continue to do it. In my free time I work on abstract software things that bring no money at all and still have half my brain there :)
I remember stealing some candy from a cupboard and my mom asked me why I stole it instead of asking for it and I told her it tastes better when I steal it.
Making $10 in a job where you are mostly getting paid to deal with other people's mistakes gives much more pleasure than making $1 for yourself.