Why don't more GM's play The Grob/Borg?

It's clearly the most underrated opening of all time. It allows for creative aggression and avoids any book preparation from their opponent. Why doesn't say Magnus show up to his next tournament and surprise his opponent with 1.g4?

Well, not sure about the fact that it's really agressive :
1. it doesn't attack any central squares,
2. it weakens the h4 and f4 squares,
3. it's not even protected after such a central move as 1...d5.

Then, such a plan as e5, Ne7, Ng6 controlling h4 and f4 is often sufficient to block any white pleasure in this opening.

But it's still fun games to play with both sides.

Regards,
Troly

1. g4 is one of those openings that offer very limited tricks and if your opponent does not know them you will feel really superior and have a fun game, but if he takes 15-25 minutes to look at the lines he will never fall for it again and all g4 leaves behind are weaknesses. but if you find some neat non-standard trick with your computer in the opening, have fun with it (until someone checks it)

Have you seen this game?

It's from 2017, but this year it's rare to see anything but 1.d4 or a Giuoco Pianissimo. I especially like 17. Kf3.

Is there something to be said about erasing your opponent's days of prep by hammering them with a Grob?

You can certainly bring your opponent out of prep like that, problem is you pay a heavy price by playing not just the worst possible first move, but also worst by quite some margin. While I don't think there is a losing White first move, if there were one it would be g4.

Now at the sub master or even sub GM level you can probably still play it since the opponents just aren't that good. But against top GMs you will suffer even with them being unprepared.

because g4 is bad opening. Marginally better than passing .
- Does not fight for the center
- does not develop a piece
- help developing pieces vert little,
- in case if short castek makes king position weaker

Here is Grand master showing whats wrong with g4. White playen is NM and plays g4 quite often
http://www.eestimale.ee/artiklid/ular/2015/kuuest-kuus-kolmas-koht

Because they are playing against the best in the world where every inefficiency in your play will be punished.

@petri999 thanks for sharing -- that was a really nice game.

It would be fun)))

but im not sure people will still play it.

Just for fun