I sat through a brief from O&D last year. The Major delivering it stated that the CSR's are all fully manned with CS Eng prior to deployment. Que chocking sound from a FofS due to deploy 2 weeks later who was unsurprisingly short of CS Eng.
That's the first reason I've heard that seems realistic but it also passed roles over to the regular such as IS support to combat support arms (roles that went to 2, 30 and the reinstated 22). So sigs strength was preserved via ditching a logical reserve policy (and having the worst record on the use of reserves - in trade to avoid the Cyprus fudges).
TA problems (which I agree exist) could be solved by forcing entrance standards (not taking everyone who comes through the door), aligning TA trades to what's required not a undeployable constantly out of date bodge, using skills already present... I.e. take the TA serious.
Nope just saying that, as a CSR Sqn, we have had to have over 30 CS Eng posted in to meet the OET. However I have seen an email recently that states we are some 270 techs over manned as well as a number of Supervisors. Where all these techs are is a mystery to me because every unit I have been to does seem to have a shortage.