Do you believe that you could implement the Airbnb interface without any CSS or Javascript?
No, I don't. It has scrollable maps, for example. Those require a Javascript-operated canvas.
What I don't understand is why it needs CSS or Javascript for the rest of the interface. It's just text and photos. An empty css with static html would be enough for that, and convey exactly the same information.
I’m also a proponent of simple pages wherever they can be made but we’re not the only audience on the internet. Different people find different UIs effective.
For example: Airbnb (last I looked, anyway) has a little mini carousel in the thumbnail of a listing. I found it mildly useful. I imagine a company the size of Airbnb are tracking if people use that widget so it’s probably earned its place in the interface.
Standing outside the whole thing with no data and saying “none of this is necessary” strikes me as an unhelpful perspective. Neither you nor I actually know.