Trivia: SPOILERS: Director Todd Phillips has defended the controversial ending, in which it is revealed that Arthur is not the Joker who would go on to fight Batman when he is stabbed and killed by another inmate, who then carves a smile onto his face. Phillips noted that the two films were called "Joker," and not "THE Joker," and stated that Arthur was the person who inspired the real Joker—presumably the inmate who killed him. However, this explanation was poorly received by fans, who felt duped.
Trivia: Despite the first film being a billion-dollar hit, within days of opening, "Joker: Folie à Deux" was already considered a bomb. Its domestic total was less than the first film's domestic opening weekend, and by the start of its fourth weekend, it had been removed from roughly 90% of theatres. At just over $200 million, the worldwide gross is only about 1/5 the original's. It is estimated that it will lose the studio $150-200 million, making it one of the biggest box-office bombs of all time.
Trivia: In a surprising (and given the reception, highly questionable) move by Warner Bros, director Todd Phillips was given complete creative control over this film, including final cut, and no test screenings.
Answer: For the most part, it was likely down to the fact that the first film was a massive smash hit, grossing $1 billion on a budget of less than $70 million. There was simply too much financial incentive for the studio to not greenlight a sequel. The director also reportedly hated that the character, as portrayed in the first film, had become something of an "incel" poster boy and was idolised by part of the audience. So he wanted to make a sequel that tore down this notion by reaffirming that Arthur was just an unhinged, mentally ill weirdo.
TedStixon