It's not the only active one. It's just the newest one. The newest usually is more active, but by and large it seems the community has more of a fondness for Seal Rock (Seize).

It's an irony that many complain about the "PvE" of Shatter, and claim they "just want to PvP", but so many hated Slaughter. . . You and I perhaps are exceptions, but many others complained about Slaughter, now want exactly that.

¯\_(ツ)_/¯