I started because of financial security, starting with news about some notable data breaches. I also learned too much about how most financial institutions handle security, which got me to realize I cannot rely solely on their guidance and instructions. I figured the next best way to prevent unauthorized access is to make it so as few people try to access my accounts as possible. The best way I figured to do that was to embrace online privacy and decentralize/anonymize myself as much as possible so that financial/professional me is not connected to online versions of me to avoid any sensitive info being shared during eventual data breaches.
After years of this, I became more fascinated in general by privacy in general, both because of the creepy factor and because I despise censorship. I believe privacy and freedom of speech go hand in hand.
Lastly, this may sound dark, but I have a thing about not wanting to be on lists. Being on a list is what helped the nazis track down and eventually exterminate Jews during the Holocaust. That lesson from history stuck with me. Anything that is fine here and today could lead to extreme suffering or unexpected consequences tomorrow or somewhere else. Privacy is the common sense hedge against that uncertainty.