What? I am answering the question: Here are some reasons that we have no discovered life yet:
A) We have no capacity to even be near half of the things we are studying, and while bigger things (like the big bang) are still easily provable and such, other things such as the literal biochemistry of a planet is out of our capability to accurately measure. In other words: There may be life and we have missed it because our tools are relatively shitty.
B) Evolution is a process driven by the environment, to assume that every habitable planet has the same natural selection factors as earth is to not understand evolution, the specific environments could very well be hindering evolution to the point where life has not evolved past unicellular life, again, mutations are what make evolution go round.
C) Relating to A, in the regards that our tools are relatively shit, there may be other factors that limit how, when, and where life forms in other star systems that we do not understand yet, so, to assume that just because we are still studying and haven't found the statistical life just yet is fallacious, because it discounts further research as well as our lack of knowledge.
D) Statistical life isn't the same as found or experimented life. In philosophy, you learn a great deal about how statistics are used to provide the impacts of an argument. There is an analogy I like particularly well: If you have two cars, a red and a blue one, and the blue one is 75% likely to be the one that was speeding, and the red one had a 25% to be speeding if we were to just use statistics to evaluate this, we would conclude that it was the blue one that was speeding. But that excludes the 25% chance you might ask, and that would be correct, but finding what is likely is all statistics do, it is the job of the thinker to support it with further warrant.
This is a rebuttal and a contention