so if all miners get lucky they can mine a block every minute ?
For as long as their luck holds out.
Eventually they run out of luck and it takes longer.
Imagine this...
I give you a standard perfectly balanced and fair six sided die.
You roll the die once every minute.
You "win" whenever you roll a six.
How often will you "win"?
Well, ON AVERAGE you will win once every 6 rolls. The usual amount of time between wins will be close to 6 minutes.
Of course it is possible that multiple times in a row you could roll a 6. As long as your luck holds out, you could keep rolling a 6 EVERY roll. Eventually you will run out of luck and it will take longer.
It is also possible that you could get unlucky and it could take 20 or 30 rolls (20 or 30 minutes) until you roll a 6.
If you get lucky enough, is possible that you could roll a 6 on EVERY roll forever? Sure. But, it isn't very likely at all, is it?
