I have noticed the same, however my conclusion is different. Typically when you read a book, your average book has more signal than your average web article or blog post. That's because more filtering has happened, like time, editors, etc. sometimes I find good web content (mostly from the top HN posts) and I don't just scroll, but I read. When I find myself scrolling the first few lines, I immediately close the link…
There's a lot of incentive to bump up the number of pages, so most of the time when I pick up a non-fiction book I end up regretting it and shouting into the void this could've been a blog post. Even in decently edited books I always feel like they could've been cut by at least 50 pages without losing any of the substance, but I guess nobody wants to publish a book under 200 pages.
Good articles are not easy to come by, but I never run out of them. The best ones are usually in the range of 30 min - 1 hour to consume, all of which could have easily been padded with fluff into a ~250 pages book, but they weren't and I appreciate that.
That isn't to say I don't read books, but about 90% of them are fiction noawadays. And I do mean read them, as I find that much more engaging than audiobooks (my mind drifts away, I lose the plot often). Good fictions are easy to find, much easier than say TV shows which take longer to consume, or worse get cancelled after a season or two without a satisfying end.