Babylon 5's near destruction in War Without End

[TerraFrost]

In the flash from the future that we see in War Without End, where Babylon 5 is being destroyed, the station is being invaded. After a gallant fight, Ivonava enables the external cameras showing Shadow vessels preparing to destroy Babylon 5 once and for all.

My question is... why didn't they just destroy it? Why did they bother with an invasion?