When I first started fingerboarding my first wooden deck was a Dooby Deck made by Ray Spartz in Minnesota and it was 29mm, I absolutely loved the shape and the size. I then moved onto the No Comply M1/M2 Shape which was also 29mm as well, loved it too. Back in the day when doing trades over YouTube were a thing, I got a Berlinwood Classic Skull in 32mm along w/ a Berlinwood 32mm Neon Colors as well, both fantastic decks with a great width.
Honestly, I believe it was ‘hype’ that actually stuck. For years, 29mm was the go-to shape but now it’s phased out with 34-55mm decks becoming a thing and 29mm becoming a phase.