Do you have a lot of vector content? Only raster images can be compressed or downsampled.
Yes, everything is either in EPS or AI for printing purposes.
I suppose that answers why it won't down sample. Is there another way to compress the PDF?
You might have better luck if you use only .ai and not eps, though it still will not compress.
Is there another way to compress the PDF?
Are you preparing the PDF for print or screen viewing. If it is for screen viewing you can force a flattened, rasterized page to any resolution, which would significantly reduce the size, but would print at the lower resolution.
So if you add a transparent object to the master pages (something at 0% opacity, make an all raster flattener preset, and export to Acrobat 4 Compatibility, which will force the flattening. Something like this:
If you use EPS with transparency, the content might be rasterized. Don't use EPS, use either AI or PDF/X-4 instead.
You should also check in Acrobat what kind of content causes the most size of data. In the optimize dialog is a button to see data use.