Print media also doesn't have to deal with: resizable windows, accessibility, user styles, navigation, mixed media, comment sections, SEO, browser compatibility, load times, or security.
I understand we are just talking about page layout, but web designers still have to simultaneously contend with everything I've listed.
You mention a solution for 3 different sizes (desktop, tablet, and phone), but a responsive site often has to subdivide further. Even so, "tablet" does not have a standard size. Rotating a tablet/phone also changes the view size.
Size is not the only usability difference between desktop and mobile devices.
Columns in such a way would likely be hell in terms of accessibility (remember, the user can change the font size).
Of course, there are (potentially) ways to solve each of those, but they will depend heavily on the individual sites' and users' needs. This brings us right back to the issue of non-standard design across sites.
I wouldn't expect well-designed print media from a web designer any more than I would expect a well-designed site from a print professional. They are different professions and problem spaces that sometimes overlap.
Instead of disparaging all web designers as unprofessional morons, perhaps consider that they balanced all of the above along with your points and still landed on a different conclusion from you.
tl;dr the user can (rightfully) control a lot of factors in how they view the web that traditional print and graphic design do not have to deal with.