To say there should be no crashes is like saying there should be no crashes of commercial aircraft. They have hundreds and sometimes thousands of hours of training and flight time before being allowed to fly us around and yet crashes still happen. There are a multitude of factors beyond the Pilot's control which can cause a crash, and this technology is in its infancy.
Take cars and commercial aircraft which have over one hundred years of technological advancements built into them and yet there are crashes each and every day that were 100% beyond the pilot or driver's control. When you have a catastrofic failure, you are often merely a spectator from that point on, and with this young technology The catastrofic failure failures happen more often than we like. Then there are the acts of god such as microbursts, lightning, bird strikes etc.
Sometimes as they say Sh** happens.