when i did complet the fallout 3 and + the last broken steel i did not get a end credits why is that?

End credits only roll if you do not have Broken Steel. With Broken Steel installed, you can play the game forever, until you want to start another character, or get bored and whip the disc at your nosy next door neighbor.

Alternatively, if you want to see the credits just click on the "Crew" entry in the main menu.