You seem to either have a fairly skewed sense of reality or didn't actually play Melee when it was the most recent game in the series. The best part of Melee was that EVERYONE liked it, casual or core. You never heard people going "Yeah I'd play that party game but it seems too fast for me," you heard people going "I can beat the **** out of Mario with Pikachu on PokeFloats!"
Your premise is inherently flawed; the idea that a casual-friendly environment and one that facilitates competition well cannot be one in the same is false. I myself played Melee casually, free for alls with items on and primarily on Hyrule Temple for several years before I even heard of the competitive scene, and I loved it. My Captain Falcon didn't know how to SHFFL, or Dash Dance, or combo, and most of his KOs were from Forward Smashes, but it was still my favorite game. The competitive scene's existence does not detract from casual players in any sense. In fact, it offers additional depth to those who are interested in taking their play a level further.
First, I played Melee from it's release to Brawl's release. Second, I think it's time for a history lesson.
Did people love Melee. Of course. All the Smash Brothers games were well liked. But, did people like competitive Melee. Oh no. They hated it with a passion. That's the difference. It seems memories grow short and no one really knows what went down pre-Brawl. Remember the Tier Wars? People didn't like hearing that their favorite character was bad and they should go to Fox. "Oh," they say. "Your using Roy? Clearly you need to move to a top tier character." It may seem like I'm joking, but this was a real thread. And this was common place. It was common for competitive Smash plays to say one character is awful and you need to change to another despite you'll never enter a tournament.
This is also why "Tiers are 4 queers" exist. Remember wavedashing? It was loathed. Ever wonder why there was always an issue of whether it was a glitch or not? It's because the player base saw it as cheating. It was always a hot button issue until Brawl's release. People didn't like it and wanted it removed. Basically, no one liked what Melee had become. Melee got lucky that it was not online. Something like this would ruin the online experience, and the reaction to the game would have been much worse than what actually happened. When Sakurai made Brawl easier to play, he did it in response to these things. Find it surprising that almost every technique from Melee was removed. Even dash dancing was removed (which had little effect on the game).
The reason a game like more, or one with more depth, wont work is because people don't want to spend that much time learning a game. People want to jump in and enjoy it. Surprisingly, people don't want to dedicate all their time to a video game. A lot of people work and go to school. People want to have social lives. And some might even want a relationship with the opposite sex. They don't want to sit down and get the muscle memory down for short hop-air dodge-short hop-air dodge-short hop-air dodge-short hop-air dodge-short hop-air dodge-short hop-air dodge. They want to play and enjoy the game. They want to hop right in and have a good time and they don't want to waste their time getting to that point. This is why games that are geared towards hardcore players do not do as well. People do not want a game geared towards competitive play.
Memories grow short, so the issues of Melee were forgotten. Competitive Smash tries to paint Melee as this perfect game that everyone loved, but the flaws were very real and people demanded a fix. I'd be surprised if anyone remembers the 4Chan raids as a reaction to competitive Smash. The changes to Smash were done for this reason.
"But why did I target it so squarely toward people well-versed in videogames, then? That's why I tried to aim for more of a happy medium with Brawl's play balance." Most people here wont get it because they can see players not being competitive. While they will say otherwise, they can not understand players who are not part of competitive Smash. This is why Sakurai said this
"Melee fans who played deep into the game without any problems might have trouble understanding this, but Melee was just too difficult."