The Dark Ages were dark for a segment of Europe. The Roman Empire was still going strong in the east. The Bronze Age Collapse happened across a much larger area.
Roughly the area of the Dark Ages: https://en.wikipedia.org/wiki/Migration_Period#/media/File:I...
If anything, the area of the Dark Ages looks to be larger than that of the Bronze Age Collapse. But either way, they're both referring to events that happened within a specific geographic area.