Maybe because some tw4t in an office working 8 to 5, no duties, no weekends and no deployments doesn't have the forethought to even consider that the easy option, of just holding back the lump sum you 'owe them' after they messed up over the last year equals hardship, difficulty in paying bills and not feeding the kids.
Oh yes, I forgot to mention the trouble that follows after bills you though you could pay bounce and you find yourself up in front of the CO with all hopes of promotion dashed.
Two points on this. Firstly, a soldier can hold his CO to account if his pay is incorrect for a lengthy period of time. And a soldier can take his employer to tribunal to regain pay he (or she) is entitled to.
I know this, as I have done it. After that clusterf*ck, laughingly referred to by MOD as Pay 2000 (in 2001), I spent over a year being incorrectly (ie under) paid. Having waited a long time and frequently visited my Pay Office to always be told 'It's Glasgows fault), I got a tad vexed.
So, I went to a solicitors. They could not believe I had put up with it for so long. In their words, a civilian would be taking his employer to tribunal after a month (if that!).
So, I wrote a letter to my CO, stating the whole sorry story and said that if the situation was not resolved in 4 weeks, I would be taking him to court. Strangely enough, it didn't come to that and my pay was sorted within 2 weeks. For the conspiracy theorists amongst you, I actually got a decent CR (for my then CO - he wrote shite CR's and had some very odd views on promotion, but that is another story).
So, the moral of the story is, don't put up with it forever and don't be fobbed off with it being some other (usually untouchable) dept (ie Worthless Down or Glasgow). Give it a few months and things don't get sorted, take a trip to your local citizens advice bureau or have a free half hour at one of your local solicitors. You'll be surprised what you can do!