Kirk and Decker didn't have that kind of relationship or trust built up, and Kirk wanted to be sure that his orders wouldn't be questioned.
Except that Decker did
question them (and rightfully so). And whatever Spock's trust in Kirk might have been, the cadets (aside from perhaps Saavik) didn't know Kirk well enough to trust him the way Sulu, Scotty, and Uhura did. They knew his reputation, certainly. But reputation and reality don't always go together.
In some ways, it's actually more surprising that there wasn't a problem during TWOK (compared to TMP) after the Enterprise
was crippled in part because Kirk was asleep at the wheel. OTOH, given that Kirk was also the only reason why the ship managed to escape destruction, perhaps the cadets realized that they couldn't have done any better in his place.
Yes, I know Decker questioned orders. But Kirk wasn't expecting him to, at least not the way it happened. And at first he had an angry reaction to being questioned. It was only later that he realized Decker was right.
I wasn't thinking of the cadets. My point was that Kirk and Spock had served together for a long time and knew each other so well that even if an order seemed a bit odd, Spock would tend to follow it anyway, given Kirk's track record of achieving solutions by unorthodox/illogical means.