Conversation so far:
When did Tom Simpson move to Brittany?
In April 1959.
Why did he move to Brittany?
his National Service papers were delivered; although willing to serve before his move.
What did he do once he moved?
He applied to local cycling clubs, and joined Club Olympique Briochin, racing with an independent (semi-professional) licence.
How long did he race in Club Olympique?
He was invited to race in the eight-day stage race Route de France by the Saint-Raphael VC 12e, the amateur club below the professional team Saint-Raphael-R.
If he accepted the race, did he win?
Simpson won the final stage, breaking away from the peloton and holding on for victory.
What did he do after the win?
After this win, he declined an offer to ride in the Tour de France for the professional team.

Question: Why did he decline the offer?
Self-contained rewrite: Why did Tom Simpson decline the offer to ride in the Tour de France?