Are there many local businesses near Stansted that are attracting workers? I think one of the problems MAN has is that it is located in a relatively thriving area, people who used to gravitate to the airport no longer need to. As has been pointed out, the race to the bottom is complete. Until MAG/Swissport/Dnata/Menzies etc start paying over the going rate and offering good incentives to keep loyal staff they will continue to struggle. Working conditions in T1 in particular are very poor. Toilets are filthy, there's are no hot food available unless you go and queue with the rest of the passengers at Burger King or Greggs. For an airport this size to have no staff canteen facilities is criminal.
It will get a lot worse before it gets better.