The judiciary is not a legislative body. I don't think anyone is claiming it is. But it acts, in practice, often as a legislative body. Certainly any application of judicial activism is indistinguishable from legislation due to the use of judicial precedence, i.e. it is parallel law-making.

For what it's worth, the nature of the judiciary appointed by representatives chosen by voters is just slow representative democracy. It is no surprise that, given the ability to make a law-like, appointed in a manner that is representative-like, they act lawmaker-like.

They are, in their activism, isomorphic to lawmakers. That's what judicial activism is. In a POSIWID sense, the judiciary are lawmakers, no matter what you call them, like North Korea is a dictatorship despite being called a Democratic People's Republic.