Yes.
The explanation only tells us that it happens under certain conditions
Yes. It's the only thing the explanation has to tell.
Why did the window break? => an explanation for the truck driving over a rock which sends it flying.
That is the explanation of how the rock ends up in the window. We could go further and ask where the truck came from, where the rock came from, etc... but it's not relevant to why the window broke. No matter where to truck and rock came from... the explanation of why the rock was sent flying remains the same.
Same here with evolution.
What triggered the process?
Well, the conditions in place of things reproducing with variation in a struggle for survival in competition over limited resources.
That's the explanation of why the process occurs.
You can off course ask where the conditions come from, but at that point you are asking about explanations of
those things and no longer of the evolutionary process.
.. it doesn't tell us why or how
those conditions came to be.
It doesn't have to as the question asked isn't about those conditions. It's about the evolutionary process.