I made some research and I 'm sure that their is a mistake but no idea where.
I found on 2miners.com that hashing rate is 6K G/s on the network
I found that a rtx 1070 has a hash rate of 6 G/s or 1/1000 of the hashing power
So it means that with a single RTX 1070 I could mine : 60x60x24x(1/1000) or 30 K grin A year !!!
at a price of half a dollar it should mean 15K dollars a year …
Where is my mistake?