requiring JS makes sense on some sites, namely those that act more like web apps that let you do stuff (like WhatsApp
I mean yes, but Whatsapp is a bad example. It could easily use no JavaScript. In the end it's the same as Lemmy or any other forum. You could post a message, get a new page with the message. Switching chats is loading a new page. Of course JavaScript enhances the experience, makes it more fluid, etc, but messengers could work perfectly fine without JavaScript.
There's a difference between "wouldn't work" and "wouldn't work as nicely". That's what this post is about :D Most websites would still work in the same basic way without js.