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 Bach's style had been superseded by (the precursors to) Classical, and sounded old-fashioned at the end of the 18th century.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).

Not hard to believe, even now Bach is considered an acquired taste

But many are acquiring it. Source: me. I have sung Bach for a living in my life. :)

“Ahhhh Bach”