Why is e4 so commonly played in the first move?

I remember Grischuk playing f4 against Wesley So, I think in the 2019 Sinquefled cup and got a draw. 

edit: 2018 actually, just checked.

Oh! Ok thanks for the information. Useful and interesting information! 

So is f4 safe??? 

You have to be wary about the weakening of the e1-h4 and the g1-a7 (especially when castled kingside) diagonals. But It is ok, can't see anyone getting better results with f4 than e4, d4, c4 or Nf3 however it's something you can play as a surprise every now and again.

Oh yes! You are right! 

Depends...

Depends on the skill levels of the players playing it.

Does the person playing it know how to play it?

Do you understand what type of middle game position you will arrive at? 

Do you understand how to play that middle game?

Their is more to openings than just memorizing moves.

And Carlsen has played it six times (one regular time control, two rapids, three blitz) with slightly above average results: 6 wins, no draws, no losses.

But of course Carlsen can make any offbeat opening look great.

Carlsen's world champion for a reason.

But sometimes opponents surprise me with 1.a4 or 1.b4!!! But that is illogical and most of the times they lose, but some times high rated plyers show off like that. 

A friend who is a USCF Expert said that in his opinion.  What separates Carlsen from other GM's is his ability to find/play the 2nd, or even 3rd. best move in a line.  While other GM's are in search of the "perfect move"  Carlsen travels the less wandered road.  If this is true?  Carlsen has a bit of Korchnoi in him.

Ok. 

1.a4 you can play either e5 or d5. Since your opponent gives you the chance to gain space at the center, then grab the center.

Ditto for 1.b4. This one actually can come with a tempo, since if you play e5 you activate your DSB and attack the b pawn at the same time. White will probably play 2.a3 and then grab more space in the center with d5.

This does not need line memorization. If your opponent lets you have the center then grab it.

Well most players are right handed, so as you move your hand towards the centre pawns, the first one is the e-pawn. Hence 1. e4
ROFL

For the 99% of us.  Thats as good a reason as any i have heard!

According to https://www.chess.com/openings 1. a4 has the highest percentage of white wins...

It has only 25 games though, so not very statistically representative

ikr a3 should be played more often

a4 is a blunder, since because you played a4, you can't play a3

it controls the midel and  it is the frst move to start 4 move check mate.

wth is the four move checkmate? i only know a one move checkmate!