New gTLDs have been released constantly since ICANN dropped the restriction. Also consider that a lot of Lemmy instances are run by individuals as a side project. That means they’ll reuse or nab whatever cool sounding domain they can get to spin up their new instance as quickly as possible.

Personal theory of mine is *.itjust.works meant to stand for “It Just Works” until they decided to give their Lemmy thing a go.