The importance of Johann Strauß

Strauß took the operetta, which was rooted in the Viennese Singspiel via Jacques Offenbach and Franz von Suppé, to a climax - although he himself had great success only with a few operettas ("Die Fledermaus“, "Der Zigeunerbaron“, "Eine Nacht in Venedig“, "Wiener Blut“). What really hurt him was the flop of his opera "Knight Pazman“ at the Vienna Court Opera in 1892. Even the overwhelming success of "Die Fledermaus“ came only after the performances in Berlin and Paris. What is beyond doubt is his unique position as a composer of waltz and dance music. 

How did Strauß come to be a composer of operettas?