I have found that in a bare bottom tank, you are right, the lbw don't live very long but in a tank with gravel, they seem to live forever until my fish dig them up.
Its pretty cool actually, the fish are smart enough to know where the currents in the tank go so when my discus are looking for worms in the gravel, they congregate in 2 corners and stare intensely into the gravel, then blow at the gravel to move it and dive for the worms when they see one.
The other really cool thing is that the discus know the moment I throw salt into the tank and the salt hits the gravel, all the worms will surface so once they see the salt, they just follow the salt to the bottom and have a left over worm feast
Not sure why the worms die almost right away in a bare bottom tank though