Starfleet had conclusively lost the battle, and the survivors, with T'Kuvma's ship disabled, got the the hell out of Dodge. With war being declared, Starfleet had better things to do then check up on an uninhabited frontier system they'd been driven out of and they'd have no reason to think the Klingons hadn't returned and to collect the ship. The survivors on the ship clearly had some communication capability: when Kol showed up, there was no surprise that T'Kuvma was dead, so word had clearly gone out. They were obviously just being ignored until Kol decided it was to his advantage to reappear: for all anyone knows, he'd been monitoring the situation so he could swoop in just at the right time, before they managed to get themselves moving and were desperate for supplies.
So, taking all this into account, the obvious answer is that Starfleet simply didn't consider the possibility the Klingons would just leave the ship stranded there, and with the pressure of the war they were too busy to bother checking an old battlefield out on the edge of Federation space that had no strategic value.