Question For You...

[Rooster]

During a fishless cycle.... taken that the tank is more or less sterile, you add amonia....

Where the hell does the bacteria come from ?

 

[annka5]

Tank isn't sterile, not in the sense of medical equipment etc, and neither is the water you add to the tank.
The bacteria are in both but in TINY amounts - not enough to convert the ammonia to nitrite , nitrite to nitrate, etc.