There is no need to invoke a more complex being to explain the universe if you don't need one to explain god.
It saves you from committing a special pleading fallacy. So it makes more logical sense to not invoke a god.
The 'god' explanation is simply appealing to mystery. People can't explain the universe so they invent a god they also can't explain.
It's really the height of intellectual laziness.
Also, 'a natural phenomenon we don't yet understand' is the ***only*** hypothesis that's ever come true.
Gods were thought to be responsible for thunder, lightning, solar eclipses, lunar eclipses, tides, earthquakes, volcanoes.... the list goes on and on.
You know how many times the god hypothesis was shown to be correct?
Zero. Not once. Not ever.
You know how many times 'a natural phenomenon we don't yet understand' has been correct?
Every single time. Every mystery ever solved has turned out to be *NOT god*. Every. Single. Time.
So we sit here now, perhaps not fully understanding how the universe came to be in this state.
And despite a 100% record of failure for 'God did it' and a 100% success rate for 'natural phenomenon'...
...Theists suggest god as an explanation and somehow still expect us to take them seriously.