I think people get this slightly wrong - he was more regarded as a performer and improvisor, and the pieces published during his lifetime were mostly keyboard/organ pieces that were considered educational. He was a pretty obscure composer but (mostly) well regarded by those in the know, if a bit too intricate for some. After he died he wasn't immediately very influential, instead he was considered very old fashioned.

From Wikipedia: https://en.wikipedia.org/wiki/Reception_of_Johann_Sebastian_... After his death, Bach's reputation as a composer at first declined: his work was regarded as old-fashioned compared to the emerging galant style.[a] Initially, he was remembered more as a virtuoso player of the organ and as a teacher. The bulk of the music that had been printed during the composer's lifetime, at least the part that was remembered, was for the organ and the harpsichord. Thus, his reputation as a composer was initially mostly limited to his keyboard music, and that even fairly limited to its value in music education.