The 14 Dumbest Things In Star Trek II: The Wrath Of Khan
2. "Damn Peculiar"
Starfleet surely knows that the Reliant is assigned to Project Genesis, so when Kirk calls them concerning Carol’s cry for help, the very first order of business ought to have been to try to call the Reliant and ask what’s what and if they know anything about it.
Nothing in the film suggests such a call happens, or, if it did, that Starfleet ever got back to Kirk about whether they could or could not get through.
Furthermore, despite being told they are - as-usual - “the only ship in the quadrant," they spot the Reliant-assigned-to-Genesis not only in their quadrant, but “closing fast.” As soon as Kirk coms to the bridge he's ordering "Try the emergency channels, so something is already odd. The moment Spock deduces that something's squirrelly about Reliant's excuse about “their Chambers coil is overloading their comm system” ought to have been the last straw.
But no.
From Carol's message earlier, Kirk knows...
a) Someone is trying to take Genesis
b) That Carol believes it's someone(s) from Starfleet ("Did you give the order?")
c) That her transmission gets "Jammed at the source"
So when the Reliant shows up acting "damned peculiar" even too-long-out-to-pasture Kirk should've put two and two together and acted with all due caution.
Yes, it’s a story point that Kirk is rusty, but given everything leading up to the moment of the ambush, his hesitation and inaction serves to not merely portray Kirk as out-of-practice, but an incompetent fool, responsible for the loss of Genesis and the Enterprise damage and casualties.
Dumb enough to warrant being drummed out of the service.