"If we're not alone in the universe, then how come no one has found us yet?"
Prime Earth is the theoretical concept that we may not be alone on Earth, but if that were the case then when or where is everything else in the known or unknown universe? The idea that our home has yet to be discovered seems rather implausible the longer we wait here as time should have allowed our discovery by now. This theory is explained further in what is known as the Fermi Paradox.
The author's own interpret of Prime Earth is that we truly are at what could potentially be the center of the universe and all of reality. The only difference is we clearly are orbiting around the Sun so perhaps that is what truly remains at the center. If this is the case, then what is so important/unimportant about us or the Sun? Our Earth's sun is going to die out many years later and destroy us, correct? Well some have speculated that the reason for no extra-terrestial nor super natural phenomenons is because there have already been countless other planets that have died before any known force could explore it or register it and we're going to be next which in turn means they cannot find us either.
On the off chance however we are not simply destined for an apocalyptic fate, some religious say that it's because a higher power has it in for us, but in the opposite meaning of that expression as opposed to a great anger (depending on the revelation prophecy). This means our plain, subtle, and predictable globe carries some greater purpose that we are yet to fathom yet. This could refer to the idea that we have balancers that maintain order roaming among us and whether they be an alien, divine, or simply a governmental experiment that they keep nature and life in check via the way of The Wielders.
Further study on Prime Earth suggests all life and realities extend from it (or at least the ones in that Prime Earth's Multiverse) therefore making it the most release and important of them all. This could also explain why nothing supernatural happens here (or at least not anymore depending on religion or faith) anymore as to protect it from being destroyed. The one thing that could make this true (potentially) is if somehow before the time of the sun's supernova that we obtain the most likely impossible super device used to reignite the Sun. The reason this is such an unlikely possibility has to due to how small the Earth is and how large something needs to be to both effect and survive long enough to alter the Sun. If we never find a way or receive a way by an external force to save our Prime Earth, then it's safe to say we're just a regular Earth inside some other Universe.