Why do some Elsevier journals use a single column format?
(Copy Editor speaking ;-) )

When designing a journal's typesetting style, there are several things to consider:


What are the paper size restrictions? Can you choose any paper size or choose from a short list, or is it fixed? For instance, Springer uses it's own paper size for many publications, The journal I typeset is stuck to A4 because it's the cheapest to print here, etc.
What font size and family is going to be used? The smaller the size, the more characters per line you get, as well, sans-serif fonts make it harder to follow a line of text in a long paragraph.
What are the typical contents of the papers? For papers with many long paragraphs, it's almost necessary to have narrow columns (I'll explain that later). For papers with lots of colour photos and graphics, you want to allow graphical appendices since colour printing is then cheaper and printer handling easier. For lots of math formulas, you prefer wide columns so that they fit better. For lots of very small graphics and tables, you might prefer two columns so that you can put more easily two of them next to each other.
Who is going to use the final template and how? Do you have a professional typesetter to carefully typeset all the papers? Do your audience use Word or LaTeX more? If they use Word, you think twice to make the journal two-column since you can be close to sure that people will mess the template up.


What is "narrow" and "wide":


Narrow is basically anything with less than 66 characters per line on average. It's been proved over centuries that this is the limit width on which the eyes are able to follow the line correctly and switch to the next line correctly. With sans-serif fonts, the width should be a bit less since the serifs significantly help to follow the line.
Wide is anything that allows you to conveniently typeset long formulas. The rule-of-thumb I know is: At least 50 characters per line on average. Remember that being too wide makes it difficult to follow the lines correctly. However, this is not much an issue if the only long text in the typical articles is the introduction and most of the other paragraphs are less than 4-5 lines.


The decision of Elsevier to make some journals one-column and another ones two-column on the same paper size might be, seeing the arguments above, quite justified.