Basically it started as a personal need/itch to scratch. Also, I'm old enough to remember when my data were my data, applications were my applications and no other entities were interested in what I do/write/see. ;) The NSA things helped my decision to do this, but I was thinking about the program from before.
I decided to open source the code after a review on the App Store (probably the US one) that basically said: "Who are you and why should I trust you". This comment hit a button inside me (and was fundamentally true).
Something else maybe?