I've always wondered this. There has to be a strong programming background, and in some cases, a strong hardware background (hard-mods come to mind). And by professional I mean those who are responsible for either finding new ways of soft-modding or develop the updates for the softmods.
Well you obviously need plenty of programming skills to make a softmod. You need to have an excellent understanding of how the OS on the wii works (IOSs etc) and you need to look for exploits. You need a bit of luck too
Many of the hacks for consoles are actually just exploits - people have found methods of running homebrew by using exploits to their advantage.