You see most high school kids use the proper technique. You watch college football and you will start to see the "kill-shot" mentality and less of the hit and wrap technique. You watch the NFL and it looks like more than 50% of the tacklers forget proper technique and want to lay the guy out with the big hit.
But I think the play in Minneapolis was a simply miscalculation by the defensive back. It looked to me like as the DB ran up to Diggs, he intended to first try and play the ball. He then slammed on the breaks so that he did not get called for pass interference. Then when Diggs jumped and caught the ball, the DB was off balance and simply had no choice but to try and dive at the legs of Diggs. He missed and the rest is history. I feel for the kid.