From what I can tell super-beginner figure skate blades (i.e., rental skate blades) are a little like hockey blades - relatively flat rockers in the center, gradually spiraling up to much more curved rockers at the ends. Of course, rental skates are sharpened so carelessly, the shape evolves unpredictably with time.
So, is there any advantage for a beginner blade with an 8' rocker? And does the following flip-flop sequence make sense
Beginner (8') -> Intermediate (7') -> Advanced (8') ?
Sort of??
A longer rocker is more stable, which beginners and those doing difficult jump landings appreciate, but which mostly isn't a big deal for intermediate skaters. It also lets you go faster, and glide longer on a push, both of which are very important at higher levels.
A shorter rocker let you turn more easily. Turns aren't needed for complete beginners, and are relatively easy for advanced skaters - though Ice Dance has more difficult turns than most freestyle, and the overwhelming majority of the world's top ice dancers use MK Dance, which has 7' rockers. (But MK Dance, and some other Dance blades, are also effectively ground thinner, which makes them faster and glide longer than the Coronation Ace and Ultima Supreme freestyle blades I've tried.)
Maybe tradition skews the statistics, because Ultima and Riedell are relatively new?
Plus, MK and Wilson give away or discount a lot of skate blades to top level skaters and coaches, which skews the statistics too.
And Ultima at least used to give pro shops a bigger profit margin (not sure if that is still true), which again skews statistics.
To complicate things even more, top level skate techs often modify the rocker profile, so what their top customers get often isn't what the factory intends. Of course, they have to remove a lot of steel to change rocker lengths, so maybe they prefer to start with something close to what they want.
But I'm not an advanced skater, barely an intermediate skater, so I don't fully understand the rational reasons for the changes, if there are any.
Of course you are only discussing main rocker, not the shorter spin rockers that are up front.