There are several reasons why abiogenesis is unobservable. The first is that if it did happen, it happened in a place and time beyond our observation. The second reason is that if abiogenesis happens current ideas of it happen to take too long to be observable. Finally, any observation of a new life where it had previously not been seen, could have numerous other explanations other than abiogenesis. They could include simply missing it before, contamination by our own actions or presents, the life that we find could simply come from another location, and there are many more possibilities. All of this adds up to abiogenesis being unobservable.
Because observation is a major aspect of science, this means that abiogenesis cannot legitimately be considered science since it is completely unobservable. The entire idea is nothing but a result of the presupposition of atheistic naturalistic materialism, not science.