Responses
massive commercial success (high sales, merchandise revenue, anime adaptations, global fanbase), flexible storytelling structure/industry infrastructure (expansive worldbuilding, battle shonen formula, magazine serialization, editorial support, assistants, hiatus acceptance etc), and last but not least, creator dedication
^ that. some mangas are written not because they have a story to tell, but because they need to continue an IP while it's still popular.
it's just work.
or, the manga is a monthly release, it just updates slow haha
How does a manga lasts for 15 years and its still ongoing??