Rotary Engine Born On This Day

On this day (1 February) in 1957 the first rotary (Wankel) engine juddered to life in a NSU laboratory in Germany. How come the rotary engine never became popular? http://goo.gl/Xqrga6

I had three Mazda's with a rotary engine and loved them. A '73 Mazda RX-3, a '74 Mazda RX-4 and a Mazda Cosmo. All were fun cars and I enjoyed tham all very much. Great little engines, but they could be thirsty.