Why are more people less prone to adding people on their Social Media, FB-Instagram?

I'm curious if you have strong boundaries on who you allow to see your social media or not. I had a co-worker recently try to add me on FB- I did not add her. Because, I left to another team. I made the mistake years ago by adding a boss and coworkers on social media, and that was a mistake.

Why are more people less prone to adding people on their Social Media, FB-Instagram?
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