The first impression of a series is always the most important, even on a mass level. Let's say, for example, they release a sequel to Delgo one of the worst and lowest grossing animated flicks of all time. This sequel, however, is amazingly well-done and gets positive reviews, but still doesn't draw as much as the original because of the very fact that the original built this reputation to stay away from anything related to it in some form or another. There's a few exceptions to this rule obviously, but for the most part applies to everything when it comes to popularity and recognition.
In Japan, the first impression of One Piece wasn't alongside the releases of Naruto and Bleach, it was alongside a whole slew of garbage manga which made people get attached to it as it had some form of a running story. And then when Naruto was first published in Japan, people were already reading the "good" parts of One Piece, and same can be said for Bleach. This release format basically gives people different impressions of these series where publishing time played a factor on which was most popular or not. When you publish certain stories at certain times, people are simply going to be attracted to it more-so than other manga.
When Naruto and Bleach was first published, One Piece already was into the Alabasta arc, which really defined One Piece as a series.