1) no universe (or multiverse) exists and there is nothing,
2) at least one universe exists and there is something.
These possible occurrences are independent and therefore have equal probability of occurring, i. e., each has a 50% chance of occurring.
Therefore, the reason there is something instead of nothing is simply because there is a 50% chance of that being so. ____________________________ In a far off none existent universe, none existent philosophers are arguing over why there is nothing instead of something. They are funded by non-existent government agencies.