It's been 20 years, and The Simpsons Hit and Run developers are just as surprised as you that the cult open-world game hasn't got a sequel yet

gamesradar.com:

The Simpsons Hit & Run was "going to be a franchise," according to its developers, who are just as surprised as us that the game never got a sequel. 

As revealed in MinnMax's The Oral History of The Simpsons Hit and Run interview (thanks, IGN), which includes insight from former Radical Entertainment developers - such as producer John Melchior, designer Chris Mitchell, lead programmer Cary Briseboi, and more - it seems no one quite knows why we never got a sequel to the beloved game. In the interview, Melchior reveals that at one point, we were going to get up to five Simpsons games from Radical but this sadly didn't end up happening. 

Melchior explains that back in the early 2000s we not only getting Hit and Run, but there was also a medieval Simpsons game in the works - that the show's creator Matt Groening had pitched - by The Lord of the Rings: The Two Towers game developer Stormfront Studios. "The biggest crime was that Vivendi [Hit and Run's publisher] did not obtain The Simpsons license, though they had an offer in," Melchior continues, before revealing that the publisher was offered a five-game deal.

"It's a really good deal and Vivendi said no, after the success of Hit and Run," the developer reflects. When asked what the reasoning behind this decision was, Melchior simply said: "I don't know." To add more salt to the wound, Chris Mitchell and Melchior went into detail about what the Hit and Run sequel we never got was supposed to have in store for players. 

"There was going to be time travel," Mitchell reveals. "We had airships, we had planes, we had lots to go on [with] The Simpsons," Melchior adds, before saying: "This was going to be a franchise, no doubt in everybody's mind" - which makes the whole thing