The other issue regarding technical and non-technical trades is the extra two ranks they have go through, SAC(T) and Chf Tech. Especially considering that when promoted from Sgt there isn't the offer of extesion to age 55, ( LoS 35 under the NEM).
The average length of time to reach FS for non-technical trades is 22 years, for technical trades this increases to 27.5 years.
The extra time spent in training for technical trades simply doesn't make it an attractive option especially when they are paid the same.