May not have been equipped with that feature. That could have been an new thing on the Intrepid Class (Voyager). Of course it's equipped, the episode "Cause and Effect" established the ship had the capability. You guys call yourselves fans when you know very little?
The ST: TNG technical manual states that the core is ejectable. Given though that they were in a combat situation, and that the core was rapidly destabilizing, it might have been damaged to the point where an ejection would have destabilized to the point of exploding, or possibly the ejection hatch may have been damaged in the battle.
Without a core a ship is stranded not being able to engage faster than light travel. So it assumed that the crew would want to explore all other possibles instead of risking being stranded in space. In addition a damage warp core creates a large antimatter explosion so it could have been that releasing the core wouldn't do any good.