If there's one big reason that even many die-hard fans of the show are not necessarily expecting a renewal, it's the lack of a clear direction for the plot.
In the original manga, the main character has lost 48 of his organs (for reference, the human body apparently contains about 78, according to Live Science), and regaining them requires a pretty epic years-long journey. However, in the new show, he's only missing 12, making it possible for the 2019 anime to come to a conclusion faster than the original manga story, which was canceled and given a rather rushed ending.
The new "Dororo" does conclude the story, but in a manner somewhat different from the original (via Monsters & Critics) — it removed a plotline that would have put young Dororo and Hyakkimaru in direct conflict and left an open-ended conclusion with a foreshadowing remark from the narrator: "Biwamaru believes that something more than blood or despair lies ahead for those two young souls," he says.
Should a second season come, it might very well opt to go beyond the story enshrined in the original manga and take the characters on new adventures.
