Continuity mistake: During the episode Ronon has flashbacks and keeps referring to "the gate" when trying to make his wife leave. It was only after Ronon met the team from Atlantis he begun using the term Stargate as most (if not all) prople in Pegasus refer to the Stargate as the ring of the ancestors.
Continuity mistake: When the Atlantis team finds out that the experiment has caused problems in another universe, McKay's sister says to Rodney, something like,"You said that the chances of connecting to another universe that was inhabited were astronomically small." It was in fact Carter that said that.
Continuity mistake: Lt. Colonel John Sheppard is packing his belongings up and his skateboard is against the wall at first, then it is on top of boxes.
Continuity mistake: After returning from the Daedalus, McKay talks to Nola about how he had been a god to them the past years. In the shots filmed from his front, the standard radio headset is visible in his ear. In the shots from behind, it is gone.
Continuity mistake: In several scenes (mostly on the planet) we see characters reacting to tactical information from the oracle as if it's displayed in real time. However, the units in the display are moving far more quickly than they could in real-time.
Answer: Because even all 4 Naquadah generators (one was destroyed) together is only enough to dial Earth for approximately 1.2 seconds (As seen in the episode "Letter from Pegasus"). Further, if Earth had found a ZPM, they would dial Atlantis and let them know. After all, the SGC has no other use for a ZPM than to dial Atlantis.
Grumpy Scot