Warning: SPOILERS for Solo: A Star Wars Story are ahead!
For most of Solo: A Star Wars Story, Paul Bethany's Dryden Vos served as the chief representative of the criminal organization known as Crimson Dawn, but he wasn't the man at the top. After his death, Emilia Clarke contacted Dryden's superior, who was none other than Darth Maul, who we hadn't seen on the big screen since The Phantom Menace in 1999. However, there were several other candidates in contention to be Solo's big cameo, including Jabba the Hutt, the giant alien slug we love to hate. As for why Jabba wasn't selected, Ron Howard attributes his absence to the folks at Lucasfilm feeling he just wasn't a good fit, as well as didn't want to feel like they were setting up Solo 2. Howard explained:
Jabba was on the list, but they kind of knew they didn't want to go that way because it would be sort of funny, and maybe a little bit too much like sequel-baiting.
When thinking about Han Solo's time in the criminal underworld, Jabba the Hutt is usually the first individual to come to mind, as Han owed money to Jabba in A New Hope, and when Han failed to make payment, the Hutt proudly display the carbonite-frozen Han on his wall in Return of the Jedi. But even though we know Jabba best for his connection to Han, it's worth remembering that he was one of the most powerful figures in the galaxy far, far away's criminal underworld for years, so it certainly would have made sense if he was the one pulling Crimson Dawn's strings. Evidently though, as Ron Howard told Empire, including Jabba in Solo: A Star Wars Story might have felt like it was teasing a sequel (which, judging by Solo's box office performance, doesn't seem likely at this point). So instead, Jabba was referenced at the end of Solo when Han and Chewbacca decided to head to Tatooine to meet that "big shot gangster" who was putting together a smuggling operation, as they'd learned from Tobias Beckett.
It's worth noting, though, that Darth Maul's cameo in Solo: A Star Wars Story could also potentially be looked at as "sequel-baiting." Those who've kept up with The Clone Wars and Rebels animated TV shows know how Maul is still alive and what his ultimate fate is, but regarding the movies, his brief appearance could lead some moviegoers to assume that he might return for another standalone Star Wars movie, even though there's no word yet on if that will happen. As for Jabba the Hutt, while Guillermo del Toro has expressed interest in directing a movie about the character, who knows if we'll ever see him on the big screen again. Maybe the Boba Fett movie could find a way to squeeze him in.