No offense taken Decarz2, it's a good question.
The reasons I use them? 1. I know them inside and out, how they play, what to expect out of each club, etc. 2. I've had great success with them so far, and I'm living by the old adage, "If it ain't broke, don't fix it". I'm sure that I'll switch out to different clubs at some point, but only when I feel I'm no longer competitive with this set, and that hasn't come close to happening yet. 3. I own all the clubs out there, and have tried them all. The Taylormade and PIng clubs are fine ones as well, but I don't find them to be any more accurate on average than the Tour Starters, and they are less forgiving. All you gain is 5 extra yards on average, and that's only if you hit the line perfectly. Miss by a little, and all that extra yardage gets erased. It might seem like you'd need more yardage on a course like Bethpage, but obviously you don't since the lowest score recorded was using the Tour Starters. The only thing I've upgraded and continued to use is the TaylorMade r9 driver. With the high winds on Kiawah and the length of Bethpage off the tee to the fairway, it's kind of a must have.
It's all about feel and what plays well for you. If you are looking for your first upgrade from the basic club set, I would definitely reccommend the Tour Starter set as your first purchase. They are pretty cheap, and give you just enough extra distance, spin, and forgiveness to be highly competitive.