It used to be the same for the individuals site some years ago, but they overhauled it bits by bits. From what I saw, the company site is also getting slowly overhauled, although it's not as high priority.

> C'est des sous menus dans des sous menus, si t'as plus qu'une page ouverte a la fois ça te déconnecte de l'autre, ...

The reason for that is that the site is basically a progressive merge-and-overhaul of many existing administrations and their sites.