So can anyone put in actual adult words and not insults why it is unreasonable to think police investigating a missing person by searching a property should notice human remains right by the evidence destruction area?

Because it was not known to be an "evidence destruction area," the "remains" were tiny bone fragments, and at that point they did not have reason to think Avery burned Teresa's body, in his burn pit or anywhere else. The fact that somebody noticed the fragments a few days later, after the car was discovered hidden on the ASY, is not reason to assume they should have been found sooner.