Joe, I think you're missing the key points that 1/ the Glasgow area has a higher holidaying population than Edinburgh so routes such as Virgin to Orlando and Emirates to Dubai (as well as the European bucket and spade destinations) will always work better from GLA than EDI and 2/ the Glasgow area has a much higher ethnic population than Edinburgh so Emirates to Asia (via Dubai) will always work better from GLA
A more than adequate explanation for your "mystery".