If Lunchables were famous for anything, it was not quite being what they claimed to be. Take the pizza-flavor variant, for example. It was actually just a cracker with some cheese and some dry pepperoni. It tasted good, but a pizza it wasn't.
Kids found Lunchables exciting because it was like making your own lunch, DIY style. All you had to do was put all the ingredients together, and you were preparing meals like a proper grown-up. They're still around today, although they've become a little more complex.