The main reason is it's strength and curse at the same time: completeness. GURPS is elaborate, and very, very nuanced. It can do almost anything in the core and there's a way to do anything else if you can't figure it right out. This is damned cool, yes. However, and this is why Savage Worlds sneaks its way back into the picture....it doesn't do the work for you. GURPS is, like Hero System, a toolkit game. It gives you tools, but lets you do the building. Unlike Hero, it lacks big fat books full of predesigned content,* which Hero at least has. And, of course, so does Savage Worlds, which is all about giving you everything you need up front.
Savage Worlds is more of what I have coined a Toy Chest game. It has tools in there, sure....but it's mostly about opening up the chest and pulling out lots of ready-made toys. It's also very much a game that's all about giving you lots of toys to work with.
So in the end, GURPS will tell me how to build my monsters, and may even offer some templated guidance....but Savage Worlds will give me the actual monsters and some simple mechanics for modifying them if I so desire. It's a subtle distinction, and worth noting that GURPS can work quite well without spending a lot of time in design, if you assume a baseline default of "reality" and make the weird stuff exceptional and mysterious. But Savage worlds is just full of quick an dirty fun....and less prep time.
Of course the good news is that I could easily run some horror using Savage Worlds with the Horror Companion, and GURPS Horror and GURPS Zombies for spicy ideas. GURPS has always been about modularity and cross-compatibility, even if it's just in the percolation of ideas.
So right now, with the limited time I have to do prep work, it looks like GURPS will take a back seat once again to Savage Worlds. SW is just too hard to beat....although I look forward to playing GURPS again when I retire some day and my son is grown up!
(EDIT: Maybe, maybe not. Verdict is still out. I've got some ideas for a modern horror game percolating and GURPS would be the best logical fit for what I have in mind. Savage Worlds rocks, but it lacks the right sort of somber mood for what I have in mind. OTOH Basic Role Playing would also work, and has the advantage of being familiar to my players. Decisions, decisions...)
|Source! And a cover for what sounds like an awesome world book too|
*Yeah some of the PDFs do this, but talk to me when they compile Dungeon Fantasy or Monster Hunters into actual print volumes (not just the first four DF books, the whole shebang) and I'll be happy to take the PDFs more seriously. Come on SJG, you brought Car Wars back into print, give GURPS Some love. Even PoD love would be nice.