This is going to be a look back at how awsome Spore was supposed and it turned out. And to answer the above question: One claimed to be scientific (evolution), the other one actually achieved it (creating a believable future).
When Spore was initially unveiled, everyone was in awe of the grand scale of the game. Not only in terms of sheer space, but even moreso that it was said that the player could really follow his own creature through all kinds of evolutionary stages. Visuals also were great, while already simple, they looked rather realistic. We also had realistic behaviour, like your creature pulling a dead creature´s body to a safe place to then eat it. Sure, some quirks were already present, such as mating with another creature, but such elements were put in decently.
So what did we expect from Spore prior to its release? A simulation of evolution, seamlessly progressing in a believable way.
What did we get? A game devided into five separate stages where you jump instantly jump on the evolutionary ladder, rather then take it step by step. Visuals were turned into some mainstream-appealing cartoon-look, and social interactions between your own creatures became complete comedy.
Basically, Spore went from a scientific vision (and just listening to Will Wright´s speeches shows how awsome he wanted Spore to be) to a mindless monster-creator with bonus-environments to put them in.
I have no idea who to blame for this. I´d prefer to believe it was EA who forced Will Wright into making these changes, but who knows. Spore 2 is probably a sure bet, but at this point, i don´t have much hopes for that game to do what people wanted from the first one. Oh well, a tiny glimmer of hope remains, as i really think that the original vision of Spore would be the greatest game ever created.