It is not the case that the ultra-right fringe parties like Jewish Power had governing power for decades. It's a parliamentary system, weirdos get elected to the Knesset, but the governing authorities --- at least prior to Netanyahu, and even during Sharon's time! --- were normies, not neo-Kahanist terrorists. It's easy to find lots and lots of political analysis about why this has happened, much of it having to do with the probability that Netanyahu could wind up imprisoned (for things having nothing to do with Gaza) once he fails to assemble a governing coalition.

See also: https://news.ycombinator.com/item?id=40421217