Who says we haven't? I've witnessed miracles, met several people who claim they have and have even seen videos and letters speaking of miracles that occured. St. John of San Francisco and Shanghai--a local Orthodox Saint from about 50 years ago, went around working several miracles, healing people, claming the tides and doing all sorts of things. And if you find the people that experienced them--probably really old by now--they would assert 100% that they experienced miracles. The problem is that all this evidence is anecdotal and we have a tendency to doubt them until we experience it ourselves.