There is another, more fundemental set of reasons for leaving kit there - I'm sure it's been covered on PPrune before.
1. A lot of this kit was purchased under UOR; as such the Treasury paid for it out of the Reserve and therefore "own" it. The Treasury effectively writes off the kit asap as the kit's support costs are met by the Treasury until the end of the Op - they have no interest in bringing it back or, indedd, paying to do so.
2. The Army could pay to bring it back, but would then be liable for all of the support costs when it's back in the UK. Guess what? Defence is broke, therefore something else would have to be chopped to pay for it.
3. If it were brought back it would annoy Industry as it would require a huge hole to be blown in future procurements to pay for it, and future support money would go offshore as a lot of the kit is foreign.
4. A lot of the kit is heavily optimised for Afg and therefore would cost significant amounts of money to mod/upgrade for a more worldwide role.
5. Leaving kit to the GIRoA is a good political win.
and, as said before, a lot of the kit is tired and worn out after years of harsh use in an unforgiving environment. A lot of stuff will doubtless find it's way into the Core Orbat but not all of it. Lazy, sensational journalism methinks....