Some people see pettiness, I see realism. If we open qualifying up to anyone, we open the floodgates to hundreds of thousands of potential claimants, with an enormous amount of work required to identify their eligibility. We further face prospects of lawsuits from those who feel they are now entitled to one retrospectively, but didnt get one.
To award it retrospectively would be an incredibly difficult thing to do (and thats based on lots of discussions with those who have a very good understanding of what that would have entailed had that been done) and been a nightmare to administer.
Far easier to make it a simple cut off date, with enough notice that those still serving know whether to stay on or not (there was a roughly 18 month notice period I recall), than go down a complex road that would satisfy few, cost an inordinate amount and still lead to OUTRAGE stories in the Daily Mail when the overwhelmed medals office took years to process Uncle Ernies paperwork due to the weight of applications.