That's absolutely true, and perhaps Fox underestimated the pull of the EPL and overestimated the pull of the A-League. If a subscriber watches both there's really nothing that tells Fox what the driver is for the subscription. Now that they've lost one it's entirely possible that a lot of people that watched A-League have dropped Foxtel completely.
In saying that, FTA audiences have gone south as well so I don't think it's entirely an EPL driven thing.
Did Fox underestimate Optus?