The French knew what the Germans had done to Rotterdam and didn’t want to see Paris bombed to ruins.
The British weren’t willing to send the RAF to defend Paris at the expense of London.
In later years, the French were full of blame-shifting excuses and explanations for their surrender, but the plain truth was that the French army had been defeated by the end of May 1940, and, having lost their best formations, was no longer capable of sustained and effective resistance. Committing the RAF to the defense of Paris after that would have been both foolish and impractical.