There are multiple incidents of major security lapses on Babylon-5.
- Attempted assassination of ambassador Kosh.
- Attempted assassination of ambassador G'Kar.
- Attempted assassination of Captain Sheridan.
- Telepathic assault on ambassador Mollari.
- The security team didn't know an entire section of the station existed.
This is not even counting all the incidents of petty theft, murder, and drug dealing on the station.
Babylon-5 is among the most important places in the political galaxy. There are diplomats and government officials and heads of state visiting it every few weeks. It simply can't afford even the appearance of sloppiness.
You'd think every ambassador would hire their own security force.
Why didn't Babylon-5 hire a lot more security guards? Or hire a more professional security force?