This is the thing that annoys me the most with Star Trek. They discover incredible technologies and then in most cases the next episode everything is forgotten.
In the TNG episode "The Nth Degree" the Enterprise with the help of Lt. Barclay's enhanced mind make a jump in a few seconds halfway across the galaxy with alterations he made to the Enterprise engines. Why wasn't this technology developed since this episode was several years before Voyager got lost in the Delta Quadrant.
Since Barclay made these changes to the Enterprise engines, why didn't Starfleet keep using it since this would seem to be the ultimate form of space travel, to instantly jump from one point in space to another without racing thru space.