Yes, they can form abiotically and spontaneously, it just requires energy input from the environment (ie heat) at some stage. Also, keep in mind that diphosphates also have energetically favorable dephosphorylation reactions, they just do not work for the biotic enzyme for DNA synthesis.

If you get too deep down this rabbit hole you are going to need a chemist to answer your questions, but here is a review of how the field currently thinks it may have happened.