There's definitively something weird marketing bullshit going on. I have a few books in an old print and a new print. The new print have larger letter and insane margins and line separation. The larger letters are great, if your eyes aren't the best anymore, I just don't get why half the page is margins.

You can have a book printed in the 1970s and it will be half the thickness, and shorter height. It has the exact same content as a modern book. At some point we went from the average number of pages being somewhere around 200-250 to over 400. You don't actually get more words, they just take up more pages. Paper type might also make a difference, I have 60 year old books with ~250 page, they are half the thickness of a modern murder mystery with around 400 pages, and the old book is hardback, the new one is paperback.

I think it's vanity, people would rather be seen reading a brick of a book, regardless of the actual content. Even if the old hardbacks are easier to handle and carry in your backpack.

When I was a broke college student I would buy thicker books to get best value.