As part of the devs farewell message on their site, they have included malicious code to make each visitor sends 2,000 requests to the dbzer0 servers in an attempt to DDOS and take the instance offline.
PieFed has a default list of domains/instances that are blocked when you do a fresh install for a brand new instance. A critical difference between PieFed and the Tesseract blocks is that any of the blocks in PieFed are completely visible to, and under the control of the admins of the instance. So, ultimately, it is just an out-of-the-box default, but the instance admins always have ultimate control over moderation/federation choices. This Tesseract stuff is taking those powers away from the admins.