One-click "methods" are just shell scripts, running on a computer, that runs the actual program that's doing the rooting. Have a phone self-root? It's probably possible, but don't hold your breath waiting for someone to start working on something. Since in probably 99.99999% of the cases in which someone wants to root a phone, there's a computer available, self-rooting isn't a very interesting problem to pursue. (There are too many "real" problems - like phones that can't be rooted at all, and can't have ROMs flashed to them. And even in cases like that, not too many people are both capable of coming up with a solution and interested enough in fixing a problem in a phone they don't own.)