It ain’t free and is sometimes not possible at all.
At work, I’m admin of everything, by Meta’s own privacy policy I’m not allowed having an account which is not mine. Not having a WhatsApp account is very hard these days. I manage to do it but it ain’t free in the sense that I’m missing on a lot of group chats I would otherwise be in, and sometimes I’m still in it via my wife. Not being on a social network also prevents me from seeing photos of me posted by someone else, where I might be tagged!
It’s never as easy as “if you don’t like it just don’t use it,” especially for social networks.
So it’s not possible because your friends won’t contact you any other way. It’s very possible not to have WhatsApp - only around 20% of the population in the US use it.
(I lived in a place where WhatsApp is ubiquitous, but honestly I don’t even know if I know someone who uses instagram and it’s certainly not used socially meaning with people I socialise face-to-face)
Instagram is the default DM platform for young adults in my experience. When I meet new people in non-business contexts they always ask for my IG username (which I of course don’t have).
In non-WhatsApp ubiquitous places, “what’s your IG?” is the standard when you meet someone in the wild. You can always go with “oh, just WhatsApp me!”, but then again you’re still on Meta. I’m talking about age range till like 35ish, probably.
Also, significant chunk of people don’t use Instagram/Facebook for posts, but just like another messaging app. I basically have my notifications enabled for DMs, and not that interested in content scrolling.
Maybe if you're a teenager or in your early twenties, and dependent on where you live. But as a thirty-something year old my social life is doing just fine without Fuckerberg and his dumb apps.