your eye needs somewhere to rest
There is a big difference between newspaper columns and web whitespace. The former are more or less uniform and easily seen (I’ve also read newspapers with explicit delineation of separate articles, and it was even better experience). The latter is just chaotic blobs of whitespace, which doesn’t usually even delineate or makes your eyes rest, it makes them lost instead. You can’t see structure, because it is so blobby. Whitespace should only surround the elements which are much more dense and “thicker” than it. Otherwise it will blend into them dissolving any structure.
I think that also has to do with "more white space = more scrolling = more ads".
Reddit is a perfect example of this. When they "updated" their UI to the current one, they added a ton of extra white space which forced people to scroll longer, thus spending more time on the site and viewing more ads. They also use a ton of other dark patterns.
When applied to the web, maybe, yes. But then there are desktop apps, and entire operating systems, designed this way.
I think it has something to do with the phones after all. Everything is "mobile first" these days (to a ridiculous degree — there's a large grocery delivery service in my city that is ONLY available through a mobile app, so they lost me as a customer), so designers have much more experience with touchscreen UIs. Desktop anything feels like an afterthought oftentimes. It's just easier to take a mobile UI, blow it up to a computer screen, or put it into a window, optionally add a dual-pane layout, and call it a day.
That, and the fact how many designers regard the result of their work as a thing in itself, an art piece to be admired, instead of merely a coat of paint on a tool that just helps people get their f-ing stuff done more efficiently and then gets out of the way.