I have only tested .edrw and .slddrw files and both have this option greyed out, Figure 1 shows this issue.  This option is greyed out for both files with multiple sheets and files with single sheets.  This issue does not seem to be present on windows OS.

Figure 2 shows the operating system that I am using and Figure 3 shows the version of SolidWorks that I have installed.

Why does Edrawings 2015 for Mac still look like 2014...has this software not been updated for 2 years or am I just using an old version?

The current work around for this is to adjust the Edrawings window until your drawing takes up the entire window which is how the current screen view works.  This gets you close to 1:1, but not exactly.

Figure 1:  Scale Option is Greyed out

Figure 2:  Operating System

Figure 3:  Edrawings Version