Hi controller,
I take it you're not a frequent visitor to the Military Aviation forum? Have a good read, it'll give you some big pointers of issues affecting the RAF today. I'd like to go into detail, but in all honesty it's all been covered ad infinitum on these forums, and if you have a look at some other forum sites you'll see that it's not just "flight crew" either. Ground trades are leaving in droves too. (Proportionately speaking, probably more so).
I really don't wish this reply to sound flippant, but there's no other way of putting it. Things are in a huge downward spiral and people can't wait to get out. Bad morale, bad equipment, fast turnaround on detachments, lowering standards, overstretch, etc etc. I could go on all night.
Hopefully that answers your question though. I'll leave you to do "further reading" as you see fit!