From what I have read:
Portals create a dead zone.
FCR 200+ Barb makes a portal.
Barb spams TP.
Because of how the frames work, the first portal doesn’t despawn.
The spammed portals don’t spawn, but STILL CREATE the dead zone.
So the dead zone gets larger and larger as TP is spammed, which can eventually cover many screens.
Monsters can’t exist in the dead zone so they die/despawn almost instantly.
When monsters thus die/despawn, their drops can be glitched giving abnormally generous results.
It’s really an exploit rather than a standard gameplay mechanic.
How does this increase their drops though