Dying from bladder cancer is actually not common. It must have been going on for years before they caught it. It is very slow growing.
BC can go undetected if the person is asymptomatic or ignores hematuria and other symptoms. It is also more common than you believe, perhaps because it often has an environmental etiology and is not as popularized as breast cancer.
However, if detected in the more invasive stages, it can appear to progress rather quickly, and the mortality rate is regrettably higher than you may think.