Why was The Treasure of the Sierra Madre initially a box-office disappointment?

Although The Treasure of the Sierra Madre (1948) is now widely regarded as one of the greatest films of its era, it was a box-office disappointment upon its initial release. According to historical analysis, this commercial struggle is attributed to two primary factors: the film's grim, fatalistic ending and the daring decision to cast Humphrey Bogart against his established screen persona in the unheroic role of the paranoid prospector Fred C. Dobbs.1