First - RPGs are a category of game that you need to teach people to play. Candyland exists for kids to teach them how to play boardgames - very few people step into a board game of even moderate difficulty without having played at least one easy board game before it. Why would you expect RPGs to be different?
That is not true. And Candyland is the gateway board game? Ok, I guess for some. I'll give you that there is a large group of people that need someone to hold their hand and teach them boardgames.
Second - there's an audience for whom the rules of an RPG get in the way of their fun rather than enhance it. If it turns out that that group is larger than the reverse then a simpler game is going to pick up a bigger audience than a more complex one. That's just numbers - and it does seem that that is in fact what has been going on with D&D's uptake over the last decade.
Sure, there are always players that don't want to worry about rules, they just want to win the game and move on. This is the mindset of the typical station cartridge video gamer. They buy the game as soon as it comes out, play it for a couple days, win the game, then toss it away and wait for the next new game. I saw this for years with all the offical D&D adventures too: they would break up, then when the new module came out, run a 24 hour-26 hour game and "go through" the whole module.
I think it's good to see a more diverse and robust RPG landscape, period. But I also think that outside of internet discussion channels, D&D still has a massive fanbase that didn't even blink at the OGL debacle.
Too true. As a News Junkie and heavy internet user, as it is my job as well as my hobby, I stay on top of things. So I was right there day to day during the OGL fumbles. Yet, on the weekend I meet roughly fifty gamers at the Rec. And maybe two have heard of it...
The problem is the D&D omnipresence and the way people are with it. A typical non gamer has only heard of one RPG: D&D. So when you ask them if they want to play an RPG, the only thought they have is "D&D". Someone somewhere sometime mentioned to them D&D was a "good game". And they want to play that "good game". You can mention another game, but they will stay locked on "want to play D&D". Even if you can get them to play <whatever> they will mostly just sit there, say they are bored, and ask when we can all play D&D.
The vast majority of gamers have only ever played D&D. They don't want to hear about any other games. A bit worse are the other group of gamers that did "try" another game, but had some sort of bad experience. So, now they will never play another non D&D game because of that. Though, oddly, they can have endless bad D&D experiences and never want to give it up.
Does it?
First, let's define "long term". To me, long-term gaming means campaigns lasting (or intending to last) for a minimum five (real-time) years, if not for ten years or even more.
By specific and clearly-stated intention, none of the WotC editions are designed to last that long. 3e was intended to go 1-20 in two years; 4e 1-30 in a little less, and 5e - while less clearly defined - seems to be more or less back to the 1-20 in two years paradigm.
But is the point of the game to "just get to 20th level and quit?" I guess some might play D&D like that, but I never saw it as that common. There are the players all focused on rules and combat. So they only play the game to get more abilities and points for their character. They think "just one more plus" will make them finally happy...again.
The long term game is not about "just getting levels", it's about a massive role playing storytelling campaign. A group of characters in for a Long Game to do the near impossible. 3X has endlessly complex rules, enough to keep a campaign going. 5E just does not have that.