For some, it’s nice to share. People encourage you to do so. I think it’s nice to others. Also a bit like in work, endorsment is nice.
I found this while working, I get paid to do a job, why should my boss tell me I’ve done a good job when I’m paid to do so?
Truth is, we are people, not jobs. We feel (I indeed) much better when someone tells me “good job”. I realised this when no one was saying it to me. This brings frustration (to me at least).
Should we share, and be nice? Yup, we are social people (I guess that’s why social networks are successful).
Your point on: are we too driven by it? Probably. I myself have spent my holidays out of social networks (still sharing some pics). It’s nice to be able to manage it. I’m also happy for people having fun or for people I care.