Trump had this as one of his campaign promises right from the get go. He gave two deadlines for a the deal to be restructured and nothing happened. He carried through on his promise, which is exactly what N. Korea took note of. There's plenty of time before the sanctions kick back in. This move looks like typical Trump. Go nuclear (Pun intended) and bring people to the table to negotiate a better deal.
Besides, from what I've read on it, in just over 10 years, Iran would be able to carry on as if nothing happened anyway.