If you like the question of "Why does anything exist?" then an obvious next question is: "What's stopping things from not existing?" In philosophy, there is a distinction between things that must be (they're called necessary) and things that may or may not be (they're called contingent). For instance, if we use the standard definition of a square, then every square you will ever encounter will necessarily have four s…
The movie doesn't cease to exist because you turned the television off, only the projection of it into those particular photons.
Top Gun will continue to exist even if you break every Blu Ray of it into tiny pieces, crush those pieces to powder, and melt the result into a formless goo.
Movies are purely information, a sequence of bits. Those bits can have manifestations such as copies on a hard drive, blu ray, or whatever. The bit sequence doesn't stop existing just because we delete every manifestation. A sequence of bits is just a very big number, and all numbers continue to exist whether we write them down or not. We can discover specific interesting numbers, such as the number 'T' that is the H.264 encoding of the Top Gun Blu Ray movie. It is 40 billion bits long, but it's still just a number. It has adjacent numbers, integer factors, and everything.
Here's the thing: the number 'T' existed before Tom Cruise was born. It existed before the evolution of humanity and will exist after the heat death of physical universe. It exists independent of time. It didn't come into existence at any point in time, or "before" time, or any nonsense like that.
Similarly, if[1] you believe that the universe follows strict, mathematical laws of physics[2], then you can imagine it as pure information, like a Mandelbrot set. Fractals in fact might be a very good analogy. They're actually very simple things, exist independent of time, and yet can produce intricate detail if you look closely. That detail may appear chaotic, but "seems" to follow oddly consistent rules, much like physics.
So this is my point of view: The Universe is "just" mathematics, and mathematics exists independent of time, making the Universe necessary. As in-universe observers, we're part of the mathematics, not any particular manifestation or representation of it. Even if there were some sort of God scribbling the bits down on a napkin that represent the state of the Universe, he's discovering the numbers, not creating them. If he destroys the napkin, the bits will not cease to exist. Inside the universe, we would never know anything had occurred.[3]
[1] Granted, this is a "if"!
[2] The more we know about the universe, the more this seems to be true.
[3] This entire point of view is the main theme of the book Diaspora by Greg Egan, which I highly recommend.