I will not even discuss many legitimate criticisms already raised in other comments - like the fact that copying has nothing to do with scientific work, and so on - since they seem obvious to most scientists (except the authors of this paper, maybe).

I would like to focus on the fact that, in papers with mathematical formulae, the information content of each letter or word is different for text and formulae. While it takes a large number of mistakes inside a text sentence to change or obscure its meaning, a single typo in a formula can completely revert its meaning (think of ">" for "<" in an inequality, or a forgotten - sign). Therefore the information content per symbol is much higher inside formulae. And the aim of a scientific article is to convey information in the most accurate way, not text. This is especially relevant for fields like mathematics, physics, engineering, but also economics, evolution and so on.

The supporting material does not seem to contain all the information on mistakes inside formulae. However, since the math page contains about 1/5 of the text of the full text page, it is possible to estimate the (average) overall number of errors inside formulae. The impressive result is the following :

Text page errors: 45.7 Word, 131.3 Latex
Math page errors: 97.6 Word, 33.0 Latex
Text errors in math page (estimated): 9.1 Word, 26.3 Latex
Math errors in math page (estimated): 88.5 Word, 6.7 Latex

It is worth to emphasize: the number of mistakes of Word users is about 13 times the one of Latex users!

This is only an estimate, of course, so it would be interesting to see the actual data, which are unfortunately not available. (I do not discriminate here between experts and novices, so Latex users have ~730 hours experience on average while Word users have ~1412 hours, that is twice the experience.)

Therefore, at least from these results, it seems quite clear why quantitative scientists used to type formulae tend to choose Latex! People accustomed to Word seem to introduce an impressive number of mistakes (more than a factor of 10 compared to Latex users) precisely in the most sensitive part of the paper, that is, formulae.

Of course, this result could be strongly affected by selection bias. It is reasonable to imagine that some selection bias could be at work, since Latex users tend to have more experience in typing equations while Word users could be more expert in typing long texts. However, this selection bias would also invalidate the whole paper.