So is that really how it works?
Some questions cannot be answered for you by others.
You state that you have the primary source material for Satanic magic.
You state that you have read what it says.
You also should understand from that literature that we have nothing to do with criminal acts or the sacrifice of living things.
We do not tell people to believe in the reality of magic.
Satanists are empiricists, in my opinion.
If you want to find out if Greater Magic works for you, then you have to verify it for yourself.
If it doesn't seem to work for you (as you mentioned), you need to determine if you really did it right or not before you assume that it can't work for you.
If you just believe in it without really trying it properly, that is not what is explained in the source material either.
I should probably repeat here that to follow this religion and consider yourself a Satanist, Greater Magic is entirely optional
There are Satanists who consider Greater Magic to be nothing more than psychodrama.
There are Satanists who consider Greater Magic to be nothing more than ceremony for ceremony's sake.
Satanism casts a wide net within which many individuals fit but not all agree on some details.
Greater Magic is one of those details.