Because when she sees both men off who are going to save the galaxy, she stays behind and does ABSOLUTELY NOTHING for the remainder of the film except come rushing back in to hug Spock (Again leaving her post for the third gawd dang time). Heck, Kirk doesn't even ask her to hail the Narada. Isn't it funny how when you give someone like Uhura a supposedly important post on the ship that she should actually do something with it?
So do you have the exact same complaint about McCoy, who leaves his post to come up to the Bridge several times, and also does "nothing" actually related to his job in the last half hour of the film, until Kirk and Spock being Pike back? And even then, all we see is him whisk Pike away to the MedBay? Yet it is implied that he's off doing his job, the same way it's implied that Uhura is doing hers--relaying all intraship communications, monitoring all frequencies for all traffic, and doing all the things a senior comms officer does (at least based on what I've been able to lean about Signals Officers in the Navy, anyway).
Uhura only ever actually leaves the bridge once (I don't count the 'lift cos she went right back up to the Bridge afterwards), and that's in the company of her captain and XO--not "abandoning her post". We don't see her hand off her station to another officer any more than we see McCoy--who is the ranking medical officer--hand off Sickbay to a junior officer.
So why do you give McCoy the benefit of the doubt, but not
This is actually what I mean--both these characters are presented in the context of their relationships with Kirk and Spock, but only
Uhura gets flack for it. Not McCoy. Never
McCoy. And there's no actual logic or rational behaviour behind a lot of it--just literally boils down to "I judge the chicks more harshly than the dudes."