I agree! You are absolutely correct to say “why waste time on Facebook”
I think it’s a combination of several things…one is that it’s a time waster (they are a big part of the problem, by designing such an addictive product). The other is that it’s so easy to sit and scroll, and not do anything else. it hijacks our brains by triggering of our dopamine system and making us addicted to the platform. It is better to do anything else (like housework or anything productive).
It’s a huge timesuck that provides us with little benefit, but it’s hard to get away from it. It’s like a digital crack and we’re all addicts!
