Despite being bordered by 3 different seas, France is large enough to have areas with a continental climate, where summers are hot and winters are cold.
Furthermore, France is more south than the UK. The same phenomenon that causes seasons (sunlight being spread on more or less area due to the tilt of the planet) causes countries closer to the equator to have hotter temperatures on average than countries closer to the poles.
And finally, France gets a lot of hot wind directly from the south, from the Sahara. By the time what's left of it reaches the UK, it was mostly stopped or diverted to the north east by the multiple mountain ranges we have. The Massif Central in particular, is right between the Sahara and the UK.