I don't know why Sakurai would do that but he did. I was one of the players who got to play the E For All demo. The game was so different.
You could dash dance like in Melee, Sonics in particular was amazing. You could waveland by doing an aerial that carried momentum low to the ground. For Sonic, Mario and Fox doing a Bair close to the ground allowed them to waveland. Pikachu could waveland by quick attacking on the ground at an angle. Crouch canceling and double stick DI worked, and you could charge smashes with the C-stick. Done things were changed about the characters too, For example: Fox's Dthrow and Peach's Fthrow functioned just like they did in Melee, Fox's fair had less vertical knock back so he could chain it into Uair, which was somewhat weaker than it was now. Ike was much slower but had significantly more power, his Aether also had virtually no horizontal recovery; less than he has now.
I don't know what happened but Brawl could have been something more than it is today. I miss the demo.