Hey, Urban Chaos was a damn cool game!

Tasing dudes until they burn.
Vire, your logic would work the same if your favourite comic book franchise was Batman and it was handed off to Rocksteady who had only done Urban Chaos: Riot Response instead of other world class developers. Many people were confused and angry at the time that a game for such an iconic franchise was in the hands of nobodies.
Developers themselves fuck up on sequels too, they doesn't need another developer to screw it all up. Hell, I thought Bungie fucked up Halo with Halo 2's mediocre single player campaign (those awful graphics, too) and they've been chasing that Halo 1 high ever since. Sometimes, a fresh set of eyes can revitalise a franchise.
There aren't many cases of a different developer making as good a game, that's true. Darkness 2 was a much better game than the first mechanically and still had the storytelling chops that you'd expect from a Starbreeze game even if it lost the non-linear world structure (but gained with adding another world). Deus Ex Human Revolution (Eidos Montreal) is not as expansive as Deus Ex 1, but it's still a worthy successor compared to Deus Ex Invisible War which was still done by the original developer and was shunned by fans forever.