Good question.
Why would anything spiritual need a physical counterpart?
The Gemorah is full of references to the physical counterparts of Gehinnom. Smoking graves of reshoim. Chochomim who searched for the entrance to Gan Eden. Korach and his sons, why did they descend into the earth? Why could their voices be heard coming from underground in that particular physical location for generations after?
Good question. I don’t know why.