L-canceling is something you should always do, but it was a glitch or unintended quirk originally. So to pull it off, you obviously had to play it the way the game "wants" you to. Or, shield exactly when you hit the ground in this case.
Since Project M is able to change the environment and mechanics... L-canceling suddenly becomes very redundant. L-canceling is ALWAYS the right choice and ALWAYS happens the same way if you time it right. Keeping it this way actually raises the skill ceiling and creates more room for error.
From a competitive standpoint: that's one way to make a heated match even hotter. The more techs you know, the better you are. It also means that's one screw up an opponent can make that you can take advantage of.
From a casual standpoint: it's just random button pushing to get an advantage and ain't nobody got time for that brb too busy having simple fun. It's annoying to constantly do or even bother doing.
From a logical standpoint: it is always the superior option when landing and it happens the same exact way every time, considering you do it right. So it makes 0 sense as to why it's just not something that happens automatically without button pushing. Or remove it entirely. Leveling the playing field (the basic mechanics) makes more sense. Fighters are unique; general game play remains uniform without ever being over-complicated.
From a gaming standpoint: it lets the users decide how fast paced they want the battle to be. L-canceling will make things hectic no matter what, because you will always be doing something as soon as possible. For a less hectic match, the delay caused by landing helps slow down the pace.
IMO I liked L-canceling because I was competitive. But... Now I'm not. The idea of creating an unnecessary skill gap is actually quite infuriating. Gaps separate players and that's to be expected. Wavedashing is a good example, since it is a very valuable tech and the result is not always the same since you can change how you slide and where you slide. It becomes dumb (and therefore infuriating to see) when it's due to a tech that technically doesn't even require button pushing to make sense.