Because nothing is precisely what does exist. But nothing implies something, so my working theory is that nothing's implied opposite something is itself the first thing, then some cellular automata like progression results from similar logical self-reference and down the line our physics (and the entirety of every logical permutation of information n-dimensionally) results from that.

A similar conception I've heard is that its like something and nothing, at the beginning of time, made a bet whether there'd be something or nothing, but the act of making the bet was already something, rigging it in something's favor. Nothing thought that was bullshit and tried to call it so, and they've been battling it out ever since.