Reason is quite simple. EPS is based on PostScript. PDF specification contains a subset of PostScript. Embedding EPS into PDF is trivial and yields high quality

Reason is quite simple. EPS is based on PostScript. PDF specification contains a subset of PostScript. Embedding EPS into PDF is trivial and yields high quality results. For a printing publication workflow having EPS files at hand saves a lot of time and problems. SVG is nice too, just needs few more intermediate steps.