Perhaps myself and the people I know are not representative of the general population, but not a single one of us has updated our 'interests' on Facebook since we first registered as teenagers. Is this behaviour widespread do you think? It makes me question how useful any data that the user has to keep update themselves truly is.
lol. first rule never assume stuff by your own character/behaviour/perspective, try to think about/find out how your target groups behave. it's KEY when it comes to marketing (in general) man....
I'd be shocked if FB interests are what you as a user liked 10 years ago. It almost certainly has to do with what content you engaged with much more recently.
In addition to engagement in Facebook ecosystem, I'm almost sure they will learn user behavior data from third party sites/apps with FB technology like pixels.