I suspect the artist for ONE Piece has a foot fetish ( WHAT HOW CAN YOU BELIEVE THAT KOLOSSAL)
Bare with me.

Knowing artists who like drawing feet, it seems likely this artist does too, given how many of their characters are barefoot, or in sandles, hell one character could manifest MORE feet, out of his feet.

Also dynamic posing. The artist does a lot of action scenes with dynamic posing centered around luffy's feet.

The last two weakest points are that he draws feet REALLY Well. If I had a deadline to draw a comic, i wouldn't focus too much effort into something as simple as a foot unless I enjoyed doing it. Otherwise he could just be THAT good.

And, Theres a lot of opportunistic shots, outside of dynamic scene building where luffy casually lifts his foot to make points, and the artist is sure to have his toes sticking out every time.

Just some thoughts haha