Because the RCN refused to listen to the RN who tried this exact experiment a decade earlier than them and it turned out horribly (they reversed it). Canada being Canada ignored them and did it to similar results, except they are too stubborn to admit it failed (so far).
Main reason I suspect was the Marine Engineers (Stokers) were red and E-Tech and Hull Tech weren’t. So they thought putting them all together would create yellow or maybe even green when it had the complete opposite effect and now it is all red.
But who could have predicted making a trade consisting of all the following trades; machinist, millwright, welder, carpenter, electrician, and plumber, would turn out horribly.