Because that is British Army doctrine at its most fundamental level. Regular or Reserve that is just the way it is and it is just a fact of life. every single soldier serving has to meet this criterion and you may be God almighty His / Herself but tough Sh1t. No waiver.Genuine questions:
On a more practical level, 77 X does not do Phase 1 or even Phase 2 training. Its skills are beyond that and you may be the most amazing spin doctor/field psychologist/broadcast ninja in the world but it is perfectly within 77 X's rights to expect that you can play face to face with the Russians in the Baltics, in winter, in some woods. Read the Reserve Forces Act 96 if this makes you go a bit pale.
If you can't soldier then you are of limited utility to the army.2: Do you consider it more important to have a broadcast communications specialist* who is ALSO a soldier 'with the same basic soldiering skills' as everyone else even if that means you only run at 50% strength?
Great. But the point about a number of defence capabilities is that they go places in circumstances that their equivalents in other more civilianised parts of HMG capabilities can't (or won't - without military support - due to risk assessments). A large part of this is because the personnel involved are trained soldiers and are therefore supposed to be able to deal with a more significant element of risk than a civil servant.* or any other number of weird 'information warfare' type roles that involves nerds and such sat on the net or making videos.
Do you see a pattern starting to emerge?