One Piece is just a less appealing show to English speakers. Long after 4Kids' dub had faded, the franchise isn't some mega powerhouse in North America. The show failed on TV three separate times (4Kids, Funimation on original Toonami, Funimation on revival Toonami). The dub is ongoing because of Toei and subsidies from the Japanese government, not because it's become one of Funimation's marquee properties. In 2017,
Fairy Tail: Dragon Cry outgrossed
One Piece: Film Gold at the U.S. box office. It goes without saying that Fairy Tail has had nowhere near the exposure One Piece has had. For starters, it's never aired on mainstream TV.*
I've always been very sceptical of the claim that 4Kids never really wanted One Piece and only got it as part of a package deal. That came from a 4Kids employee, who didn't work for the company when they worked on the show. The other series he mentioned as being part of the package aren't from the same companies as One Piece. Frankly, the idea they got it by happenstance doesn't jive with what we know. One Piece was a desired property. We know of multiple potential suitors that weren't 4Kids (notably, Funimation). Why would Toei award it to a company that wasn't really interested? In fact, if 4Kids weren't interested in One Piece, why did it land a mass-market toy deal with Mattel and had video games? That wasn't something they expected to come and go like Fighting Foodons.
*Granted, Stampede would later do better than both, but it had a wider release and benefitted from those event runs becoming more well known.
"I like the money it brings in, but Dragon Ball Heroes is the worst. That's actually the real reason I decided to start working on new material. I was afraid Bandai would make something irredeemably stupid like Super Saiyan 4 Broly." - Akira Toriyama, made up interview, 2013.
