The point of the set isn't to see if I'll wreck you, the point would be to show you what it's like to fight the stage while someone who isn't a ****** is trying to hit you. Also, many people think they play seriously regardless of money, but actually putting money on the line guarantees it basically.
Pictochat isn't "active" in the same way pirate ship is. Pirate ship may only have 4 or 5 different things it throws at you, but they are frequent, random, cover a large portion of the stage (with one exception), and every single one will probably kill you if it connects almost regardless of your %, or at the very least put you in a terrible situation that you will very rarely come back from. Pictochat on the other hand is very predictable, transformations don't repeat until it cycles through all 20-something odd forms (the number of forms outlasts the timer), each form always lasts the same amount of time, and very few forms actually try to damage you, almost all of them are simply layout changes, and even the worst one that damages you has set knockback and ambiguous DI so you're basically never at risk of dying or being put in -too- bad of a position. In other words, it's manageable, and its one actually-random aspect is trackable. As for Halberd, it's much less active in general, and although it can kill you, all its hazards are so painfully projected that it's almost not worth mentioning.
It's not even a matter of the stage being more abusable, it's a matter of playing safely and waiting for the stage to kill the other guy for you. You can't do that on Pictochat or Halberd.
Also referencing inexperience is important because, as I said, "stage awkwardness" isn't really about your personal comfort/familiarity, and I don't think there's a way to explain it that doesn't involve you playing a lot for it to click. As a side perk, actually having experience helps convince people you have a clue.
Although I can only speak for myself, "a new way of having fun" is probably the best way to describe it. For me personally I always intended to play Brawl competitively since before it came out, but I used to play Smash 64 as a kid all the time (obviously senseless buttonmashing) and memories of that inspired me to look for something deeper with smash. So I guess it's a bit of everything. I think you'll find most competitive players are willing to mess around with random stages and items from time to time, though.