Universal is terrible at their branding. As phenix stated, Shrek is probably the only popular character among the families coming to the parks. I mean, they have popular characters, like, say, Spiderman, but they aren't as directly associated with the Universal name as Mickey and the gang are to Disney. I mean, they've tried making Woody Woodpecker their mascot, but honestly, where the heck do you ever see Woody Woodpecker? I don't see him on TV anywhere, or any of his cartoons being released on DVD. Same with Popeye and Betty Boop.
I mean, people like these characters and movies, obviously, but the problem is that Universal doesn't have anywhere near the same marketing strengths that Disney does in selling their product, or more specifically, associating their product with the company name. Everyone know that Disney=Mickey....and in some cases, to Disney's benefit, people associate pretty much any animated feature with Disney, including Shrek. (Which is sad...but probably true)
I'm not saying I like that this is happening. I wish people would look into things more closely. But thats the way it stands, anyway