They can’t admit that man, because then the whole jig would be up. If life can’t arise spontaneously from non-life, then it doesn’t matter how many planets, stars, and galaxies are out there. There would be no point to space exploration unless we can find some very valuable resource that would be economically feasible to haul back to earth.
As long as they keep up the assumption that life might spontaneously arise from nothing, then they can play their probabilities game and pretend like we might find something out there, if we just look long enough and hard enough.
I for one don't think it was ever about life on other planets, it was always plunder on other planets. Wait, that would be a great title for a B film :)