They probably expect to release them in drips over many years. The most enthusiastic fans will want to own every single "lost recording". To get the max profit

They probably expect to release them in drips over many years. The most enthusiastic fans will want to own every single "lost recording". To get the max profit they might release a new "collectors item" boxed set with a lot of known material and just a few of the "lost recordings", and the fans will buy it. They are probably waiting for the opportune moment, which is when the band members die, since this will create renewed buzz around the band, and "lost recordings" are more interesting when the band is dead.