A fish in the sea in the deep ocean has a lure that lights up to attract mates and prey. Why would it need this in adaptation

One example of a fish in the deep ocean would be the anglerfish. It has adapted to create bioluminescent bacteria which allow this fish to glow in the dark. For this example, why would it need this in adaption? It uses this technique to lure prey out of the darkness and close enough for its razor-toothed jaws to strike. Along with bringing in potential mates.