There are many theories as to why the 4th edition of WOTC failed to interest many D&D players and apparently failed to meet the sales goals WOTC set for the game. My theory is simple, 4e's lead designer Rob Heinsoo wasn't really designing a new edition of D&D, but a game that played the way he thought D&D was going to work back in 1974 when he was ten years old and had read about the game in Military Modeler magazine, but had not yet seen -- let alone understood -- the rules to D&D. Rob starts off a "Spotlight Interview" on the WOTC web site (March 13, 2009) clearly stating that in response the first question of the interview about that changes he wanted to make to the D&D system when he designed 4e:
My goal designing 4th Edition was to make a game that played the way I thought D&D was going to play, back before I understood the rules.
I read about D&D in 1974 in Military Modeler magazine and bought the game by mail order. I'd read The Lord of the Rings, but not The Hobbit. I was ten years old and I didn't fully understand the D&D rules for another year or two, but I loved the feel of the game and its fantastic open-ended universe. I wanted epic battles and characters who could fight like Aragorn or Legolas or Gimli or Gandalf using powers that suited those characters. I wanted my 'fighting man' to be as tough and heroic as John Carter of Mars.
Given Heinsoo's stated design goal for 4th Edition Dungeons and Dragons, I don't see why so many people have trouble understanding why many D&D players found that 4e just did not feel like "D&D" to them. Heinsoo admits he wasn't trying to design a new version of D&D, but a set of rules that played the way he thought D&D should be played before he understood how it really was intended to be played. This would be like someone who expected soccer when he first heard of American football revising the rules of American football to be the game he always thought it should be. While many people might like the new rules, there would likely be a large number of people who did not think the new game felt much like American football regardless of the fact that it still used the American football name.