[greazy]

I believe (no evidence) that printed text is easier to read because of the mono spaced serif fonts used.

The serifs are visual cue to lead the eyes onto the next letter or word.

[duskwuff]

I don't think you mean "monospaced". Monospaced fonts (where every character cell has the same width, like an old typewriter) are almost never used for normal text in Latin scripts.

[greazy]

Thanks for the correction. I was thinking of proportional spacing.