Why do the female characters from One Piece have the same skinny hourglass figure?

Question

I've seen various female One Piece characters having the skinny hourglass figure as Eiichiro Oda's art progressed, What is the reason of why these characters have the same skinny hourglass figure?

Answer 1

If you read the SBS segments of the manga, you can get an understanding of why.

It is Eiichiro Oda's preference to draw women with an hourglass figure. Oda has repeatedly dismissed/ignored criticism from female fans for the way he draws women. Oda pretty much demonstrates no understanding of the concerns behind these criticisms and has stated vehemently that he will continue drawing women with the hourglass figure. He often tries to justify his position by saying stuff about the dreams of young boys, as here in volume 78:

D: We realized that Robin has huge breasts. We checked from the side, and Nami also has huge breasts. Why do they both have such huge breasts? And could it be Oda-san's preference?

That was a question from us two 10-year-olds. P.N. Sakucchan & Yuzu-chan

O: I keep saying this, but I'm just bringing the young boys' dreams to life! All of humanity on earth! I command your breasts to grow~!

In volume 79, we get this regarding hourglass figures from Oda:

(I only draw this kind of body, so I get a lot of complaint postcards from my female audience. Let's all stay strong and keep on living life.)

See also these SBS segments:

https://onepiece.fandom.com/wiki/SBS_Volume_57

https://onepiece.fandom.com/wiki/SBS_Volume_78

https://onepiece.fandom.com/wiki/SBS_Volume_79

Slightly related SBS segments:

https://onepiece.fandom.com/wiki/SBS_Volume_41

Further reading:

https://www.animefeminist.com/choosing-toremain-strong-against-female-criticism-the-vindictive-storytelling-of-oda-eiichiro/