Because everything we know about this universe needs a cause, nothing in this universe is causeless, so you can't simply say that "something" inside that universe is causeless.
And everything we know about life screams causality, from the need to eat and drink to generate energy, to sex for reproduction. If life can actually be causeless why is it so fragile and dependent on so many things to keep itself from death?
> A cell is much simpler than anything capable of inventing the universe.
A cell is also not capable of creating itself out of nothing.
Your lack of knowledge/understanding about how can something create the universe is not a justification for assuming that it created itself.
You need a causeless cause (otherwise we wouldn't exist), so you either choose it to be the universe itself (which is a wild guess with zero evidence and hence not even scientific as you claim), or it is God (and yes you can't and will never understand how it is the first cause)
I'd rather believe in God and his messages to us that brought actual evidence, than believe in an unconscious universe creating itself with no evidence.
Of course, belief in God is an emotionally charged topic. Many people rely on their belief for many things, and trying to argue against it is seldom productive - I'm hesitant to engage for that reason. You're free to believe what you'd like. But, since you've brought up "evidence"
I don't agree that there is more evidence for God creating the universe than there is for some kind of spontaneous event. For a start, the existence of the universe is extremely verifiable, much more so than God - no matter how much you believe in the "messages". For another, the universe appears to governed by very simple rules of physics (although not quite simple enough for my "several bits" threshold of acausality, just yet). Attempting to explain a fairly simple phenomenon that definitely exists with a very complex phenomenon of uncertain existence doesn't seem to add any explanatory power, and in fact just multiplies entities unnecessarily. All you've done there is take the mystery, put it in a box labeled "God" (along with a bunch of other things), and then said we're not supposed to look inside the box.
Addendum - I don't think the universe needs a "cause", per se - causality is related to the arrow of time, and that is a property internal to the universe. That's not to say that nothing needs explaining, but I think we should focus on "simplicity" rather than "causality".
It's much more honest to say "we don't know yet".
Fortunately, there's an abundance of evidence that complex phenomena can (and do, more often than not) arise from simple rules. Apart from this being the goal of all physics, at which it has been wildly successful, we can find examples all over mathematics. The cellular automaton "Rule 90" is a nice visual example of this: the rules are only a few bits and the initial state is a single cell, but the behavior is a tantalizing mix of ordered structures on the micro scale and chaos on the macro scale - a suggestive metaphor for our own universe.
If you saw a picture of a section of Rule 90 without knowing what it was, and tried to explain it, which explanation feels more satisfying? A mathematical rule + initial conditions that fit into a few bits? Or "someone drew it in an image editor because they thought it looked pretty"? Which has more predictive power?
If you're happy to entertain a causeless cause to explain life, why make it an intelligent designer, a very complicated object? Why couldn't life itself be the causeless cause? A cell is much simpler than anything capable of inventing the universe. All 'intelligent design' does is move the problem (and amplify it).
I think an intelligent designer feels simpler to a human because "conscious entity" is implemented as a conceptual primitive in our minds, for obvious evolutionary reasons. The idea of a non-corporeal mind spontaneously arising feels more plausible than a single-celled organism spontaneously assembling, because we need many more symbols to represent the latter. But it's a misleading perception.