Life didn't have to start on Earth. It could have started on any one of an unbounded number of worlds. It's only in retrospect that this world seems special.
What's the probability of spontaneous formation across an infinite universe?
If you mean panspermia specifically in respect to earth it's a lot more bounded in space and time to the parts that were close enough to interact with earth, but if not then yes there is probably anything that can be represented by atoms out there somewhere or other.
In an infinite universe even events with probability 0 can happen[1], but it's hard to find this explanation satisfactory. Any hypothesis that raises probability of abiogenesis to make it likely to happen at least in the observable universe looks more satisfactory than "but it could have happened anyway in an infinite universe despite being totally improbable."
[1]https://en.wikipedia.org/wiki/Almost_surely