I studied chemistry (both organic and inorganic) decades ago at Uni, and I remember learning about isomerism, and that all DNA is left hand spiral. Back then, the lecturers didn't have a definite answer to that. So I probably know more than the average Joe, but am no expert.
I started writing a lengthy explanation, and then thought, "what's the point".
The link given by notsurewheretogo appears to deal with part of the abiogenesis issue. I would add that one possible (indeed obvious) explanation is that DNA molecules form so incredibly rarely that the first DNA molecule that formed would have had a massive head start on any subsequent one that formed. I could add numerous paragraphs to explain this in detail, but...
More importantly, because DNA chains are so lengthy, it is impossible for the descendants of any DNA life form to have DNA spiral in the opposite direction.
In simple terms, all DNA life forms have left hand DNA, because all DNA life forms had one common ancestor.
Whatever way you look at it, this is actually (further) proof of evolution. Maybe a "creator" created the first DNA molecule, but certainly hasn't controlled the process since.