First of all, there's no room for him. As long as Pablo Sandoval gets in shape, and Freddy Sanchez remains injury-free, third base and second base are occupied. There is of course, a vacant starting job at first base, but that will likely go to Aubrey Huff. Many fans might wish to see Uggla starting at third instead of Pablo, but I'm sure he'd put up similarly great numbers -- he could easily hit above .300 with solid power (maybe 25 homers).
Secondly, he's costly. Uggla will likely get $10MM this year and then his contract is up. So what do the Giants do then? Sign him to an extension? He already turned down a 4yr/$48MM extension offer from the Florida Marlins, so what does this mean? He could make a huge dent in the Giants payroll for the next several years.
Third of all, his defense is atrocious. His career UZR/150 is -4.5, but in recent years, his defense has gotten even worse. He'll likely move to first base within a few years. That's huge. The reason he is so valuable is because his offensive production is rare, coming from a second baseman. If he moves to first base, he loses a lot of that value. Also, the Giants have an up-and-coming first baseman in their farm system by the name of Brandon Belt. The Giants probably want to have a spot available for him when he's called up to the majors -- rather than occupying first base for the next four to five years.
This isn't even including what the Giants would potentially give up to have Uggla for one year. They'd likely have to part ways with one or more great prospects -- a myopic move for any GM of a team that has just won the World Series.
So anyway, there's no need for Dan Uggla. The Giants could get great offensive production out of Pablo Sandoval for a much, much, much lower cost. And Uggla is expensive -- it would not be wise for the Giants to take on his contract unless they're going to make him an everyday player. Lastly, his defense is just bad. If they were to put him at first base, assuming they don't re-sign Huff, there will be no room for the promising Brandon Belt when he receives his call-up.
