Not a historian, so my answer will be simple. At the time when Russians were gaga, so to speak over France and French things, the French language was the "lingua Franca," meaning that it was the prominent language used in business and such. Draw comparisons to today's world where one can get a "bigo macu" in Tokyo, and American things and words are integrated into cultures around the world. Same scenario between France and Russia at that time. Russia was,, with the exception of St. Petersburg and Moscow, kind of an unknown "backwater." The high society elevated itself by speaking French and integrating French culture where it could.