If one does not accept an ultimate design concept, then logically this non-arbitrary clumping of particles into every increasing complexity makes for a mystery.
The how is the same, the result is the same, but the why is different.
As far as I can see, if the universe and the things in it have properties, as we see that they do, they will exhibit the behaviours that follow from their properties. If the properties had been different, the outcomes would have been too. How could it be otherwise? Why should anyone regard it as mysterious? The fact that something is complex is no excuse for thinking that it is magic.
We can study the hows and the results. The question of the whys may indeed be meaningless. More a trap for the gullible than anything real.