The utility is not of existential importance. Yes, you can uninstall Facebook, Instagram and WhatsApp, and the sky will not fall, life will just go on.
A lot of small businesses use these platforms for outreach. Without them they wouldn't have an avenue to reach and stay in contact with customers. An example would be a potter showing their work on Instagram and then linking back to their Shopify website.
Big tech literally has fingers in every single pie imaginable and it's real money for a lot of people, unfortunately.
Strange argument, you could say the same for almost anything.
Similarly to how you can just eat less and lose weight.
My neighbors and school parents all coordinate via WhatsApp. The sky will not fall no, but if you don't join those groups you wouldn't know about upcoming HOA meetings, school events, important forms to fill etc.
Facebook is useful for bigger communities like moms groups. We found babysitters that way.
One of my social clubs tried to skip out of social media and was originally meeting in person, calling each other etc, but information just fell through the cracks as the club got larger.