I feel that the lack of pay isn't the whole thing of leaving - or joining, for that matter!
The great and good of HMG and MOD have, through the systematic withdrawal of perks, privileges, pay and prospects, inevitably turned the former armed forces "Career" into a "job" that people quickly become bored with.
Add to that, the extremely slow promotion path of the RAF ground trades and lack of recognition for jobs with responsibilities and you have the almost perfect formula for driving people out as soon as they possibly can.
What's worse is that the armed forces are now perceived as a low paid job that can regularly put you in danger of being shot, in an unfriendly place too...nothing like the computer games at all!
Finally, I believe all this comes from people at HMG, living in the Chelsea/Notting Hill bubble and having never served in the forces or never had a proper 'career' before moving into politics - i.e. today's professional politicians and the pseudo politicians in MOD.