Why is it so much easier to attack with 1.d4 ?

With my bad experiences against the french and the sicilian I find it hard to coordinate an attack when you start with 1.e4. For example, in the sicilian your white square bishop only defend and your dark square bishop has no targets. 

When I play 1.d4 I notice that all my pieces can get an active role and target the opponent king and the attack easily flow...

What are the reasons for that ?

Ask Kasparov....he said the same, that after 1.d4 was more easy for him to conduct an attack. Then this stupid Kramnik showed up, developed the QGD and Kasparov couldn't attack the same...

The atrocious Berlin defence took his title in 2000 London but that's the half-truth. The other half is that after 1.d4 life is no easy...either.

Conclusion; It's not about the opening...its about the practical play. You make a move, your opponents do another one...and the best one wins. The rest are for the chess.com forums to spend our time...

Very nice view

I play 1. d4 now as a repertoire, but I used to play 1. e4; I believe this to be better because as black it is easier to transpose after e4 than d4. Additionally, the Queen behind the pawn after d4 just feels like an added bonus. However, you should play whatever fits your style more comfortably as I believe d4, e4, Nf3, and even c4 as a first move can lead to many solid games, many of which are attack-oriented.

I play e4 and I attack just fine...

Weaker players tend to have no idea what to do against 1.d4.

No one gets an attack after the first move. It depends what black plays.

For lower rated players, perhaps they're more easily able to find attacking schemes after 1.d4 because some 1.d4 systems feature a solid center, which can make flank attacks the order of the day in any position.

I think getting control of the e5-square so early is what I like about the attack

When did he say this?  Do you have a quote?

that is not even close to reality. Two examples to attack the Najdorf

- in the 6. Bc4 Fischer- Sozin line White light-squared Bishop does most of the attacking, often aiming to sacrifice on e6 (if Black doesn't know the correct move order those sacrifices are usually winning the game early for White)

- 6. Bg5, the "old" main line (with or without the Poisoned pawn). The dark-squared Bishop attacks and pins the f6 Knight, supporting f4-g4-f5-g5 and all the rest of the pawns storm.

When White plays 1 d4 I often play 1...c6 and White often responds with 2 e4 to control the center. When I replay 2...d5 I've got the Caro-Kann Def. I like and White is playing a 1 e4 game where he wanted a 1 d4 game.  Of course, 2 c4 and various other moves result in 2...d5 and I've got the Slav Defense, the Caro's cousin.

Both Defenses can lead to very closed games or wide open games.

White's playing a Caro because he wanted a Caro, perhaps?

I'm a lower rated player and never played d4 really but I reckon lower players gravitate to e4 because of that guy who said best by test.  I should start learning d4 just so I know what good counters there are for black.