It makes sense they'd nerf Wavedashing though, which is why I'm not surprised. I use it all the time (Luigi is my main after all!) but I knew it couldn't last. Here's my thoughts on it:
1) The design of Smash that makes it so unique is that instead of focusing on the player's skill with doing a complex set of sequences with their controller, it focuses almost entirely on the metagame. Performing moves is easy - only 1 button! Its all about how you use those moves, positions, predictions, mindgames, and so on that make Smash unique. I wish more fighting games did this to be honest. WDing was a complex set of buttons not too dissimilar from the moves other fighting games have that involve multiple button presses with correct timing to do.
Sakurai knew you could slide like that but probably did not think people would use it the way we do - he likely thought it was just a neat thing you'd do every once in a while, almost accidentally, while dodging an attack. When he realized how much it was being used, it started to mean that being good at the metagame was not enough, you had to have this technical skill to go with it to truly compete. To some players who could otherwise have the mindgames and metagame skill to be real pros, it was out of reach because they just could not master the finger dexterity for SHFFL'ing or WD'ing.
However, he saw how people enjoyed these techniques. So, he removed them but changed things to make it less necessary - lower traction when landing from air attacks, much quicker dodges, automatic L-Cancelling, etc. Things that are similar to the advanced techniques but usable by everyone. Shifts the focus back to what made Smash great and unique in the first place - easy to do everything in it, but difficult to truly master the nuances of how every move interacts with every other move to outplay your opponent.
With these, it maintains the whole design theory behind Smash - concentrate on using the moves your character has in the best situation, rather than having to learn complex button sequences in order to compete.
2) Wi-Fi. If you know much about network latency coding in action games, things would be easier without L-Cancelling and complete control over dodge direction. Basically, the less control the player has to change a predictable motion suddenly, the harder it is to deal with latency. By air-dodging continuing your current momentum, prediction algorithms work better. By having a landed air attack have the same lag recovery time regardless of whether or not you pushed L, the algorithms work better. The less variation possible once the player has started a move, the easier it is to make it work smoothly over the network.
I believe many of the simplifications are because of one or both of the above 2 reasons, including the change to air-dodging, L-Cancelling, auto-sweet-spotting, grabbing ledges that are behind you, auto-combo by holding A, homing tether recoveries, faster dodges, longer hit-stun on multi-hit moves (helps with the network stuff), nerf to double-jump cancelling, and so on.