It's a shame that Wikimedia couldn't donate money to Phabricator for it to stay alive, considering it raised ~$30mil in 2019.
My impression is that the developers (or perhaps the remaining single developer, as mentioned elsewhere in this thread) has lost interest in maintaining it, rather than been unable to continue.
It doesn’t seem like there is much interest in finding ways to keep phacility alive.
Note: I work on phabricator at Wikimedia. My opinions do not necessarily match those of the foundation and I’m speaking from personal experience not from any position of authority.