Probably because it doesn't try to. Sigh! One more time! The theory of evolution deals with how species are descended from other species; not how life originated.
But Prof, you said this:
There are no particularly worrisome gaps in the modern theory of evolution, barring the gap at the very beginning of life.
Perhaps I read too much into this statement. It seems to acknowledge a "gap" in need of an explanation.
As for species descending from other species: Darwin, I'm told, drew many of his insights from selective breeding experiments. But none of these have ever shown descent of one species from another. I think when he got to Galapagos, and saw the concentrated, rich riot of birds and reptiles of so many different species running around this isolated piece of geography, he drew the perhaps unwarranted conclusion that they must all be related somehow by line of descent. (That's a speculation on my part.) But what "looks plausible" ain't the same thing as establishing a fact.
So, forgive me, but I'm a skeptic; for me, the "jury's still out" on the issue of species being derived from other species. I don't think this sort of thing has ever been observed. But it makes for a great "just-so story."
I am convinced that evolution is a fact, however.
And so, we get back to where we always begin, you and I, Prof. Though I sincerely respect your right to see things differently, and to disagree with me.