Yes, D&D is too hard. In fact, if the DM does anything else except actively alter the game world and game play in favor of the players, D&D is 'too' hard for most players.

A LOT of games do such things as: House Rules that favor the PCs(max hit points is a common one), allow the players to freeze game time to get ready, always let the players 'go' first in an encounter, The DM role plays zero agression from any foe, plot armor and keeping things very simple. This makes things quite easy for the players, but that is why they are done.

Using bland by-the-book foes and giving the players just about all the game related information are another big one to make for a smooth easy game.

And using just about no tatics, terrain, environment, or common sense is another big one.

In such a smooth game, foes just walk up to the PCs to be targets for their fun.

Now, please, please, understand that there is nothing wrong with ANY of this: it's a perfectly fine way to play the game.

For example, lets take a group attacked by some foes like orcs. In the easy smooth game the orcs simply walk over and attack...after the players have gotten ready and acted first, of course. But consider:

A ranged attack: this is just a very simple tactic. The orcs shoot arrows from a good range away. So round one is the players screaming as their characters get hit with arrows from ''they don't know". Right here, this alone is too hard for some players: to have thier character attacked and they had no near automatic way to both know about it and avoid it and even more so prepare against it.

Add in torrent/environment: To even just have the orcs up in trees or any high ground is way too hard for many players. Not to mention if they were on the other side of a river or cliff side or if the PC are say crossing a bridge over a river.

'Two' encounters: Endgame here, as the orcs split up into two or three groups and shoot arrows from more then one direction.

The above ranged orc attack can be very low challange rating wise, but still be way, way, way to hard of an encounter for a lot of players. And the above encounter is still very simple. And it's nowhere even close to an impossible to win encounter......but it's just too hard for many players.