There could never have been a time at which nothing existed. If there was never a time at which nothing existed, then it's not the case that "once there was nothing, and then there was something". Atheists are not forced to explain how something can come from nothing, because nothing never existed.
It seems many religious apologists are obsessed with the BGV Theorem, seemingly convinced that it provides irrefutable evidence that physical reality has an absolute beginning at the Big Bang. But does the BGV Theorem really show that the universe definitely began to exist?