Conversation so far:
When did William Cullen go to the University of Edinburgh?
In 1755 William Cullen become Professor of Chemistry and Medicine at the University of Edinburgh.
Why did William Cullen go to the University of Edinburgh?
William Cullen was enticed by Lord Kames to become Professor of Chemistry and Medicine at the University of Edinburgh.
How long did William Cullen teach at the University of Edinburgh?
William Cullen was appointed sole professor of the practice of physic, and he continued at the University of Edinburgh until a few months before his death.

Question: Why did he leave Edinburgh?
Self-contained rewrite: Why did William Cullen leave the University of Edinburgh?