By late May/early June it was clear Trump would be the nominee. From June 1 to August 18 he held no events in MI. Over this same period he went to Florida 5 times, North Carolina 6 times, Virginia 2 times, Pennsylvania 5 times, Ohio 3 times. They only went to Wisconsin once. Clearly they had their eyes on PA and OH from the start but not the rustbelt more generally. In total, they held Trump rallies in Florida 25 times, in Ohio 14 times, in Pennsylvania 14 times, and in Colorado 10 times. He only held Michigan rallies 6 times and Wisconsin rallies 5 times. The push in Michigan didn't start until 1 week before the election. Trump held 4 Michigan rallies in 8 days (See below). Prior to this 11th hour push, it seems they were instead hoping to flip Colorado. They sent Trump there 10 times but only once in the last 8 days. Michigan (6 total visits) August 19 (1) September 30 (1) October 31 (2 events in 2 different cities) November 6 (1) November 7 (1) Here's the list of Trump campaign events. Also there was a New Yorker piece by John Cassidy which quoted Trump campaign workers as saying the big final YOLO push in Michigan was a response to polling. It really seemed to surprise them. I don't think creativity had anything to do with it. They were just keeping their eyes and ears open and wisely jumped on an opportunity when it presented itself.