What is the advantage of the two-column journal format? I am a mathematician whose work often connects with physics, so I often have to read papers in physics journals. I find that the two-column format popular with physics journals annoying, and based on the following questions on this stackexchange I am not the only one that feels that way:

Difficulty reading scientific papers in two columns

How best to present long equations in two-column papers?

Do two-column format journals publish one column for special cases?

I contend that the two-column format is impractical for long mathematical equations and is harder to read, since your eyes have to move in a pattern different from most other printed texts. But I suppose that there must be some advantage to the two-column format, given it is so standard in some branches of academia. But I can't think of a single reason why it would be better than a single column printed page! Enlighten me, please.
There's a widespread belief that shorter lines (fewer characters per line) are  easier to read, because the eye doesn't have to move as far horizontally from the end of one line back to the start of the next.  The left edge of the text (assuming left-to-right languages) may already be in your peripheral vision.  Thus it's easier to visually find the correct line to read next, and avoid accidentally rereading the same line or skipping lines.

This is the justification for the extremely wide margins that LaTeX uses by default in one-column styles, for instance.

I don't know offhand if there is research supporting this belief, but maybe someone can fill me in if they know.

Two columns makes it easier to have short lines, without resorting to small paper size, large font sizes, or huge margins.  Thus you still get a high density of text per page, and it keeps page counts down (and the associated costs).