Because it is easier to use Renard for everyday purposes. And Von kettlebopper etc is part if the title, for formal things. The other names are my middle names, all males in my familly will have one of those as their first names. My first name is not actually sean, its one of the others, but I do not like it so prefer sean, which is actually derived from jean, another name I do not like.
I will dig out Grand-Paters jackboots tonight and pay you cackling buffons a visit for your neutering 😈