Jump Street franchise producer Neal Moritz reportedly blocked the planned crossover film with Men in Black from happening because he did not want to take a pay cut on his usual producing fee. As far back as 2014, Sony was considering the possibility of combining two of their more recognizable IPs, and the project remained in development for a number of years. Director James Bobin even signed on to direct in March 2016, and the movie was given the title MIB 23. Despite having a few key pieces in place, the film struggled to get off the ground and it was ultimately scrapped in favor of the soft reboot Men in Black: International.
Members of the creative team, including Bobin and Jonah Hill, chalked it up to the difficulties of mixing the two properties. While both are genre comedies, Jump Street specializes in R-rated meta humor, while Men in Black leans more towards four-quadrant, PG-13 spectacle. There's no denying the filmmakers might have struggled finding a way to make the crossover work, but it sounds like there was something else at play that prevented it from happening.
In THR's report on the behind-the-scene woes that plagued Men in Black: International, it's said Moritz (a producer on the two Jump Street films) "refused to compromise on his customary first-dollar pact." Apparently, MIB 23 required heavy hitters like Steven Spielberg, Walter F. Parkes, Phil Lord, and Chris Miller to "forgo rich producing deals," and when Moritz refused to budge, Sony just decided to move on.
The end result of all this was the aforementioned Men in Black: International, which looked to revive the MIB franchise by injecting new blood with Chris Hemsworth and Tessa Thompson. Unfortunately, the film was an all-around disaster, getting panned critically and bombing at the box office. Even though International was the cheapest MIB movie to make, it's unlikely to turn much of a profit or spawn the sequels Sony undoubtedly envisioned when they green lit it. Though the concerns about combining Jump Street and Men in Black's brands of humor are understandable, odds are MIB 23 would have made for a more interesting film - if only to see how the premise was executed. One of the primary criticisms of Men in Black: International was that it was a bland offering that didn't bring much of note to the table.
With Men in Black: International floundering at the box office, there may not be anything Sony can do to salvage the property. There's clearly a lack of interest, so it wouldn't make much sense to try to run it back at any point in the near future. As for Jump Street, that franchise appears to be in the rearview mirror as well, as the hilarious 22 Jump Street credits sequence makes it borderline impossible to formally move forward with another installment. Fortunately for Sony, they have a Jumanji sequel due in December, which should be a hit. They're also banking on Bad Boys for Life and a new Ghostbusters to be their 2020 tentpoles, so hopefully one of those fares better than Men in Black.