Because OCR is expensive (to write as software and to process for the end user) and very error prone, especially if your text is anything other than a 12 point black font in on a white background with no formatting (italics, underlines, etc.). If my document's information is valuable, I'm not going to be willing to rely on the quality of my recipient's OCR software to get a digitally readable copy of my work. I mean, at the very least, what if they're blind?
The general hatred for PDFs in the tech community is almost completely rooted in Adobe's initial decision to make PDF editing and creation cost $500. You have access to a document that want to make changes to, but you can't because it's a PDF and don't have access to the document source because the owner/publisher didn't provide that. It's a PDF because PDFs make documents that look the same everywhere, even when printed, which is and will remain critical to the purpose of publishing documents. Well, images don't solve this problem, either, because you still can't edit text in an image, and now you lose the ability to be sure about how they'll print (margins, scaling, etc.).
Furthermore, images, even compressed, are significantly larger than a well made PDF. For example, I've got a 6,700 page document of special ed student progress reports that include detailed, full-color charts and graphs of student progress with respect to goals. It's 60 MB. 8.5 KiB per page.
Then again, I imagine it won't be long before someone mentions LaTeX as a viable alternative, even though the one thing LaTeX isn't is portable. But LaTeX is primarily popular in the tech community because it lets programmers pretend to write code while they're actually writing documentation. Nowhere else will you find people telling you to use a set of programs that require a build environment when someone asks about the best home office application to use. (Yes, I know that LaTeX is a typesetting language. My cynicism is that some tech people tell others to use LaTeX when they're asked what word processor someone should use.)
Edit: Clarified second paragraph.