Is this really a big deal to people? Playing a demo more than once?
Well, yeah. Maybe I want to play again now that I know what I'm doing & feel like I did a better job/get a better grasp of what the game has to offer.
What if there's multiple pathes or stages?
What if there's more than one character to try out?
What if I heard there's some secret or something I didn't discover before?
What if I want to keep going back to it until I can afford the actual game?
It's more of the fact Nintendo finally put out a normal demo via normal means. No restrictions, no "special version", no distributing demo codes a week early via random people then everyone else can get it later. Don't get me wrong, 30 plays is a large amount, but when it's like 10 plays for certain types of games (Project X Zone, a RPG you need to play a few times to get the hang of what's going on, had FIVE), then it starts to become more noticable.
At least something like Sonic Generation's demo, which was only available for a few weeks (& you couldn't play it after that period until a new demo was out), allowed you to play as many times within that time period & it was more of getting feedback from players on how to improve the game.