I think it may seem like Torx has more sizes than say Phillips or flat-headed screws due to the fact that with those you can generally get away with a screw driver that is "close enough" in size, whereas with Torx you really need the exact size the screw is using.
If you want to strip your screws, you can do that. And then there's the Pozi vs Philips thing that people tend to get wrong. Torx is kind of a pain in the ass because you always try the wrong screwdriver first, but it's still way better than philips/pozidriv
It's because philips drivers are wedge-shaped. They properly fit a range of screw heads. This means that there's only two or three commonly used driver sizes. With torx the sides are parallel so the driver size is directly related to the screw head size.
Also, Torx takes the guesswork out of determining which bit to use. If it doesn't fit, it doesn't fit. Phillips can be a pain in the ass to figure out which bit to use.
edit: Also, you said Hex and I'm assuming you meant Torx (since GGP did). But that could very easily be a bad assumption, so I apologize if it is.