The problem was, as often, that works fade out of fashion quickly and are put aside. Bach's style had been superseded by (the precursors to) Classical, and sounded old-fashioned at the end of the 18th century. It didn't take very long for it to be rediscovered, though: some 80 years. Rediscovering isn't even the correct word: the tradition was kept alive, but a bit underground. Mendelssohn got his inspiration from his teacher (Zelter), who had a profound love for Bach, and probably also from his aunt Sarah Levy who had studied with Bach's eldest son (W.F. Bach) and supported another (C.Ph.E).