Yeah. Remember, when Kingdom Come was written, it was being written as a possible future for the DCU as it extremum at the time. And at the time, Hal Jordan was dead. (If I recall correctly, it was written not long after Final Night, when Hal sacrificed himself to restart the Sun.) The writers didn't like Kyle, and both John and Guy had been sidelined; so the only Green Lantern left was Alan.
Note also that Kingdom Come kicked off a Renaissance at DC: it was after KC, and largely because of it, that Morrison got to do his JLA series, reverting the League to (the contemporary versions of) its original roster. It's also what triggered the formation of Young Justice. Arguably, Young Justice was one of the divergences that prevented the DCU from going down the road that lead to Kingdom Come, as they showed the younger generation of heroes going down a different path than the wanton violence KC's younger generation.