I guess that is due to multiple factors. One Piece Characters have more depth than Dragonball characters and villains. In fact, DB characters have no depth at all, the series itself revolved around strong guys wanting to fight, conquer and bust planets. It's just that at the time, Dragonball was a very iconic anime which inspired future animes. It was simple but powerful, creating an identity around being a warrior. That's all.
Back in the day, One Piece was also pretty iconic. It's just that being a series that is going on for so long, it obviously fades at some point.