The IHME model is what Trump is using to justify opening the country. The reason the model bounces up and down should be easy enough to understand. It is always easier to look back in the past when all the data is known, then to be in the present with new data coming in daily. Lets see what would happen to any model, and treat is as if each day or time period is a addition to the data, then as if it was already there. I would expect that any model would suffer. Good enough right now is better than perfect six months from now.
The point of the article is that it's not good enough.