.....and because the PM told MoD to do it!
Barring the marinisation costs the rest shouldn't be too bad. Aircrew and engineers convert onto new types all of the time and it will be a question of osmosis rather than wholesale transfer (assuming that process starts now). Re-location of the hardware to Yeovilton should not take too much effort. The Junglies already know the role they will fulfil so no costs there. And presumably the sims will stay at Benson for the foreseeable future (the Junglies already go to Culdrose for Seaking sim time).
Sounds like a mountain out of a molehill.