...because the likes of City Jet (Gothenburg), Finnair (Helsinki), Lufthansa ( Hamburg & Munich) have invested substantial sums in developing routes over the years & building up traffic for a predatory EZY to step on developed routes & dilute traffic.
This happened with Berlin, when BA connect flew a E145 twice a day for years. Then along comes LCC Air Berlin with a B738 & then also LCC Jet2 come along with a B733. Result 4 flights a day to Berlin = over capacity = all three airlines pulled off as unsustainable, leaving no flights. This situation could very easily happen to the Gothenburg route.
Of course EZY can fly where they like. However, it's not difficult to find out how many people fly MAN-BER or MAN-VIE via an intermediate stop & thus these two destinations would be more useful than diluting existing routes.
BTW, who says the new routes are going to be from Manchester? It says Northwest & as the LPL & MAN machines are fully utilised, it has to be from overseas bases or W patterns.