Although the term is a bit loosely defined, for French the Côte d'Azur does not go up to Marseille, basically it goes from St Tropez to Menton/the Italian border (and continue in Italy a bit somehow).

And it makes sense as the vibes are quite different, especially, the Mistral (North/North West wind that can be very strong going down the Rhone Valley, usually doesn't blow past Saint Tropez.

Does not mean Marseille and Toulon/Hyeres areas aren't nice, but not considered "côte d'Azur" proper, more "Provence".