Conversation so far:
How can the lyrics of Cross Road Blues be interpreted?
In the simplest reading, Johnson describes his grief at being unable to catch a ride at an intersection before the sun sets.
Why would Johnson grieve over being unable to catch a ride?
He expresses apprehension at being stranded as darkness approaches.
Did Johnson at some point want to be picked up in the cross road blues?
Yes, the song opens with the protagonist kneeling at a crossroads to ask God's mercy, while the second sections tells of his failed attempts to hitch a ride.
How else can the song Cross Road Blue be interpreted besides a persons grief?
The lyrics have been interpreted as a description of the singer's fear of losing his soul to the Devil (presumably in exchange for his talent).

Question: Why is it speculated he sold his soul?
Self-contained rewrite: Why is it speculated Robert Johnson sold his soul in cross road blues?