Because evolution is a process that takes hundreds of thousands, even millions of years to take place. Which means that we can't actually observe it taking place. Which means our only evidence for it is forensic, and therefore open to subjective interpretation. Which means that you have to essentially take our particular interpretation on faith. So stop asking questions, you creationiost whackjob!
/s
Nobody who actually observed the murders of Ron and Nicole gave testimony implicating OJ Simpson, and all they had was forensic evidence subject to subjective interpretation. I don't see why people sneered at the jury for acquitting him.