Problem with massive Gerber files from Eagle
In Eagle, the copper "polygons" are made up of many parallel overlapping traces.  If the polygon's linewidth is set to something small, like 1 mil, it quickly consumes large amounts of data when converted to Gerber.

If you change the polygon's linewidth to something thicker, it will solve this problem.  However, it also affects any thermals tied to the polygon, and can cause the polygon's borders to change.

If you need your current polygon settings, then I would suggest that you make a small-width, detailed polygon where it is important, and make a larger, coarse one over the rest of that layer.