The advantage of EPS over PDF? And why so many journals ask for EPS alone?
The eps format used to be the only possibility for including graphics in (La)TeX. Now the more modern alternative is using pdflatex, which also supports other more common graphic formats natively (such as pdf).

Most journals have outdated LaTeX processing pipelines, so they are still using eps. (And, frankly, they have little incentive to get more modern, since they are in a strong oligopoly position.)