I plan on writing my senator about this! I think part of the reason is that GM doesn't want competition to its brands. The H2 would compete against the Escalade and the the H3 would compete against a myriad GM SUVs including the Traverse which Auto Week says GM spent a lot of R&D money on.
http://www.foxnews.com/leisure/2010/04/08/gm-closing-hummer-despite-offer-table/?utm_source=feedburner&utm_medium=feed&utm_campaig n=Feed:%20foxnews/latest%20(Text%20-%20Latest%20Headlines
When deregulation hit the airlines in 1978, many airlines sold their DC9s for scrap metal instead of selling them for much more to a start up airline that would use them to compete with them. Big companies will do almost anything to stifle competition and raise profits. Perhaps GM would get 100 million in a Hummer sale, but what would it cost them in lost sales down the road?