You only need a few pictures to fill a profile. Taking a few snaps when doing interesting stuff likely spread over months or years isn’t “documenting every second of our lives”.
Practical suggestion: you can ask. Someone takes a picture with you in it, say "hey, you mind sending me that?" Like lots of social things it's not automatic (which, you know, Facebook was for a few years, and that was nice), and you have to "put yourself out there" a bit. Most people won't say 'no', and the thread with the photo is an opportunity for further interaction, if you want it to be.
or
“Hey let’s get a selfie.” (Do young people not say this anymore?)