Because if the reaction is bad, it will make them look like fools for ever greenlighting the pilot.
And if the reaction is good, they'll be under pressure to greenlight a whole series, even if they would rather do wrestling or vampires or wrestling vampires.
That why networks never show backdoor pilots unless they've already decided they'd be willing to do a whole series, and the backdoor pilot ratings are just the last hurdle for the show to clear.
Otherwise, its a no-win situation for them. Presumably, SyFy has written B&C off at this point, otherwise they would have done something long before now.