I once thought the same way as Darth Hideous on this, but have come to change my viewpoint. I'm gonna go through my own thought process on this. Hope it helps!
It's been established that a player can get a fully playable experience from a single Core Set "right out of the box," so why do I need the additional cards that a second provides? The answer, obviously, is I want to be as competitive as possible, which means having all the options at my disposal. The next player might be content with purchasing only a single Core Set, but not me. I don't do this in Magic -- why not?
Money. In Magic (or L5R, or Yu-Gi-Oh!, or whathaveyou), I spend my time opening card packs, hoping I pull something good or can trade for what I need; or in the singles market where, provided there are copies of the card available, I build my masterpiece card-by-card. Either way, this requires a heavy investment of time (unless I'm netdecking in which case it's someone else's masterpiece that I hope will work just as well for me), and more importantly, money - lots of money. All this is to ensure that my deck is able to destroy its competition. And it probably won't, since I play mostly for fun, but I still want my deck to be strong so I know that if I lose it's my screw-up, and not my deck's, that cost me the match.
Sometimes, I'll find out that the deck I've been meticulously planning over the course of a month, while strong, doesn't quite match my playstyle. Or it does, but I'm in the mood for something different. Too bad. I've spent a great deal of time and money on this deck and hell if I'm gonna let it sit in my bag doing nothing for any length of time. For a completionist like me, this drives me CRAZY! I could spend $900 and get the full playsets online, but then by the end of a cycle I'll have spent thousands of dollars for cards that won't even be legal for standard tournaments in two years.
Now, with that said, let's look at Star Wars: The Card Game. As I spend a few minutes looking at cards, I begin to notice ones that do things I like, and immediately an idea forms in my head. I don't have to go online to explore this idea, because I spent $80 - much less than the price of a single, random box of Magic - to buy two Core Sets and have a full playset of all the cards that are available to anyone. And I will never have to do this again, because the Force Packs and big-box expansions will each come with full playsets. I also got a metric ****-ton of the various tokens that are used in the game, so if I misplace a few, it's no big deal.
I like having options. But I also like having stuff in my wallet. With this game, I can have both.
Plus it's Star Wars.