>>20965486People prefer exclusive bragging rights nowadays. Having something in alpha, beta or in an exclusive demo that others aren't able to get makes people think they are that much cooler.
Smash Bros will stay Smash Bros. Sure the characters/stages/items change, but the gameplay stays similar. Those who are offering to buy a demo already know they want the game, but they want bragging rights of being able to play the demo when someone else can't. The 30 tries limit is sufficient to decide for anyone to like it or not on the open demo.