Akira Toriyama's Dragon Ball is one of the most iconic and long-lived franchises in anime. Despite beginning decades ago, it continues to leave its imprint on anime fandoms in the East and West. One of the lesser-known facts about the series, however, is that its most popular entry was meant to end a lot sooner than it did.
Dragon Ball Z was set to conclude multiple times throughout its run, but its growing popularity made Toriyama change his mind. One supposed endpoint was the Cell Games, with the series officially capping off with Goku's second death and Gohan being the hero for a potential new series. Though ending with the Cell Games could've made sense thematically, the series' return to old wells afterward means Toriyama was right to continue.
The Great Saiyaman
The arcs immediately following the Cell Games pivot to Gohan maturing into Dragon Ball Z's protagonist, becoming a hero in his own right and shifting the focus away from the old generation of Z Fighters. This shift in focus included several new concepts, such as the ability for fighters to fuse together, new Super Saiyan transformations and a refreshed identity for the series in general.
On paper, this seems like the perfect time to refocus the series or even end the official Dragon Ball/Dragon Ball Z title and switch to something new. What these new concepts lead into, however, quickly makes rebranding seem a lot less logical -- while also showing how the Cell Games and what came before it may have been the franchise's peak.
By the time the Buu Saga nears its climax, Gohan has been defeated and eventually sidelined by the return of his father Goku. Goku and Vegeta are ultimately the heroes of the saga, with Trunks, Goten and Gohan having to be rescued in order to stop Majin Buu. This emphasizes a return to the old protagonists, with the promise of a new generation of Z Fighters quickly being squandered.
The same would go for the series' first sequel, Dragon Ball GT, which overlooks Gohan in favor of a de-aged Goku as the hero once again. It also involves a dramatic time skip even greater than the one from the Cell Games to the Saiyaman Saga. Starting a new series after the Cell Games -- only to start another new series within two or so arcs -- would seem ridiculous, especially if time skips and new faces were the justification for it. To be fair, GT wasn't created by Toriyama and is considered non-canon, but it should still be considered a factor in whether or not its predecessor should have ended earlier.
Then there's the official sequel Dragon Ball Super, which also features many new concepts and characters. Its main focus is the multiple universes and cosmic gods introduced at the beginning, and Goku is again the central hero. Having the Saiyaman Arc be the beginning of either GT or Super would be a waste since both series and even the Buu Saga would quickly move away from its tone and scope.
If anything, the few stories focusing on Gohan are an anomaly, as they certainly didn't become the norm. Thus, ending or starting a new series around this outlier wouldn't make any sense from a marketing or narrative perspective, and would have ultimately been a waste of time in the grand scheme of Dragon Ball.