If the algorithm's nooks and crannies were fully known, website owners could manipulate it to display their results at the top, which may not be in the web's best interest.

I'm not OP but my guess is that without the revenue generated by the proprietary algorithm, there wouldn't be enough money or incentive to keep improving it.

With an open source google algorithm there would be possibly 1000's of lesser google's (lesser as in inferior search) the lesser googles might even get eclipsed by Bing or some other proprietary search which has the resources to improve it's search.