Why does or did Elsevier make PDFs grey and therefore unfit for printing?

This often happens when a document uses the CMYK color space and the black is set as (0,0,0,100).

When you go print in a monochrome environment, the document's color information is converted to grayscale first. Because black ink on white paper can't actually create gray, a halftoning process is applied, where the shades of gray are hinted at by using a circular-like pattern.

Because CMYK (0,0,0,100) black isn't seen as being as black as it gets, in the conversion process, it gets turned into something more like 90% dark gray, and the halftone pattern appears.

Probably somewhere along the production process, someone got their blacks mixed up, and if it's consistent with all their PDFs it could be in the scripted part of the process, there's an issue either between color spaces (CMYK vs RGB) or a conflict between the source documents and the imported parts.

guifa is correct in their analysis of why this happens, but I would like to note that there is often an easy fix available once you know what is going on and so long as the PDF is saved as text rather than as a scanned image.

When you go to print from the PDF, click Properties from the Print menu, and on the advanced tab hopefully you'll see something like this:

Under your printer you'll hopefully see Document Options -> Printer Features. If so, you may have a "Print All Text as Black" option (hopefully you do), and this is Disabled by default. Turn it to Enabled and try printing an example of the dotty-page you were getting before.

If the page is actually text and not just a scanned image, you will now hopefully enjoy a print of pure monochrome, crisp black text. This problem is quite common especially with older monochrome laser printers, as they attempted to accurately print the "less than 100% pure black" using the only tool it had available - black toner. With this option enabled your smarter monochrome printers will understand that you don't want an accurate portrayal of the text - you want a readable one!

This option will cause a problem for text effects that use a gradient, but honestly outside of the print-proofing world I've always turned this feature to on by default to produce nicer text prints.