They don't, they do initially after a wash, but after a few hours wearing them, they stretch out a bit. All jeans do this.
Levis do have a range of shrinking jeans. Don't see the point personally. I don't want tights haha.
I kinda dislike that the jeans that fit me best are some of the most expensive around haha.
Shrink to fit is a throwback to the past when Levis 501 would shrink, it's more to do with how they age/fade. Levis switched to sanforising their jeans
especially for the 502 and 505 range as there was an issue with shrinkage and the zipper fly.

