Quite simply, the aircraft going to GWY can be put to better use on other routes. As MAN and NOC are also starting, and Logan aren't exactly overcrewed or carrying spare aircraft, the simple decision would be to pull an average performing route for a better one.
Don't think competition had much to do with it. SNN-PIK is an extra 100 miles on the road if someone wants to get from GWY - GLA. Bearing in mind the LOG fare from GWY wasn't exactly excessive I doubt it was a major factor.