What made js bach famous?

Answer 1

Johann Sebastian Bach was known mainly as a keyboardist during his own lifetime, not as as composer. A small group of his students (and their students) and other connoisseurs (mostly in Berlin, where his son CPE worked) kept his music in memory during the second half of the 18th century, for both aesthetic and pedagogical value. The greatest Classical composers, at least W. A. Mozart (later in his career) and also Beethoven, studied his music and were partially influenced by him, as were prominent early Romantic composers Felix Mendelssohn (who pedagogical lineage traces directly to Bach), Frederick Chopin, and Robert Schumann. All these composers' styles become more contrapuntal after studying Bach's music. But still J. S. Bach was not widely known, not until the mid 19th century.

Wikipedia says the next part best:

"Bach's reputation among the wider public was enhanced in part by Johann Nikolaus Forkel's 1802 biography of the composer.[62] Felix Mendelssohn significantly contributed to the revival of Bach's reputation with his 1829 Berlin performance of the St Matthew Passion.[63] In 1850, the Bach Gesellschaft (Bach Society) was founded to promote the works; in 1899 the Society published a comprehensive edition of the composer's works with little editorial intervention."

Bach's works became more widely performed. An example: Mendelssohn performed Bach's works almost exclusively when he gave organ performances. As musical scholarship grew in the 19th and then 20th centuries, the greatness and skill of Bach's compositions became better known and appreciated.

This is just a partial answer; many things work together towards J. S. Bach's current status.