I live about 90 minutes from Plainfield, WI, where the Ed Gein murders happend in the 50s. Gein was kinda the loose inspiration for Leatherface. He never used a chainsaw, and only killed a few people. But he did make a suit out of human skin, and they found furniture made from bones in house. He had made lamp shades from skin, and necklaces out of ears. There was also plenty of human meat in the fridge.
So I don't know if that's the reason, but these movies always seem to get to me more than most slashers. Growing up, it was always this urban legend-like story. But it was true. some of the details changed for TCM (like the state it happened in), but it's just craziness. There have been few people that crazy since. I mean, looking at how awful the world is today, Gein's actions still are abhorrent to us. Imagine how it must have effected the 1950s, Leave it To Beaver, malt shops and sock hops America.