of course matter can pop out of nowhere - it happens all the time, see
Virtual Particle. What is different here is the vast scale at which it happened, and where this phenomon applies to the origin of the Big Bang
Don't throw away a theory because you don't understand how it is started. The Big Bang Theory is simply stunning in it's ability to
explain almost everything in the know universe that we observe. It is up to someone else to work out what may have triggered it.
This is just like Evolution which brilliantly explains almost everything we see in terms of life as it is. but evolution is not
Abiogensis
When you understand that Evolution and Abogenesis are different things, as are sex and embryology, you will also understand how you mixed up the Big Bang Theory with another
area of study which is about multiverses, unverse bubbles, oscillating universes, God's Poke, and other interesting ideas that are today all still in the realm of speculation - because we have no way yet of seeing which of them could be true.
Big Bang cosmologists work on what is observable and testable and predictable.
Big Bang cosmologists are not expecting to find out how to create a big bang, but describe what happens after it occurs.