As quoted in the article from Presidio Trust board member:
“If it’s your land, you can do pretty much what you want,” Bechtle says. “But with public land, there is just a higher level of scrutiny.”
The trust developed design guidelines for the site. The building could be no higher than 45 feet; as for looks, the trust didn’t want a building that replicated an old-fashioned architectural style...
...in short Lucas proposal didn't meet the guidelines and he didn't want to compromise.
Personally, I think the museum is a fantastic deal and any city would be blessed with the gift -- still hoping SF & Lucas find a mutual agreement (one of which not be exclusive to Lucas items/curation).
Yes, Lucas wants to create a monument. Building it in the middle of nowhere where no one will visit doesn't serve that purpose, but then it doesn't really serve the public interest either. I do hope that some reasonable accommodation can be arrived at in a location that will give many people access to the art.
Some folks have to do great things to get monuments built (Lincoln). Others donate money and let others have a say in what edifice gets built (Smithson, Carnegie, Mellon). Still others build their own edifices but buy the land on the open market (Trump, the Sears Tower). Lucas wants to build his own edifice on prominent public land, all while retaining complete control for himself. That's his problem.
But honestly. I think constraints like that are just a bargaining chip in San Francisco's social power game, where Lucas has the money and the political support but not the elite social pedigree of San Francisco's philanthropic set (who in turn suffer an inferiority complex relative to their competitors on the east coast): http://www.greenwichtime.com/bayarea/place/article/Major-pla...
Let's not forget that right now the site is occupied by a sportswear outlet and 20 years ago was little better than a parking lot. Tech billionaires show more interest in space, hospitals, and vehicles (perhaps because those fields offer quantifiable metrics of success) so I wouldn't hold my breath waiting for someone to come along with a check & collection for a more obviously highbrow museum in a city that's already amply supplied with such options.
If he wants the museum to happen, he'd better withdraw his big, fat thumb from the pie a little, and let someone else determine just how much of his personal art collection qualifies as "cultural treasure".
You have to figure that there's at least one person in every major American city who has seen the Star Wars Christmas Special, in addition to all the people who "have a baaaaad feeling about this," after seeing the movies he has directed personally, and the "enhancements" made to certain works for their DVD release.
That's why all the cities want to know what exactly he's going to put into the museum, and replying "that's proprietary information" just raises a huge, Hutt-sized warning flag over the whole project.
Besides that, I just visited the Art Institute of Chicago a few days ago, which sort of anchored my expectations for "art museum". No city wants to green light a project expecting "art museum" and end up four years later with "that useless, ugly building full of m-f-ing Gungan codpieces and Ewok hats."