it's not just for birds, it's also for fish who think they're birds.
I think that maybe the tilapia has evolved so much it thinks it might just be able to fly someday, so they keep trying. Gotta love that spirit.
BTW, they really can live a long time on the ground, I found a jumper that was totally stiff and decided to try reviving it by swishing it in the water. It worked. That fish was stiff and utterly lifeless when I found it, and after getting some fresh water over its gills for awhile it woke up and wriggled away, seemingly none the worse for wear.