Well, let's look at the milestones in North Korean nuclear testing. A critical one happened in 2016 (September 9th):
North Korea announced that this is a successful test of a warhead that can be mounted onto a rocket.
Prior to that, they had nuclear bombs but they couldn't launch them with missiles. Note that they are still improving their missiles. That's what they are testing now. And improvements come more incrementally in missile range than in device development.
Some of the North Korean threats came in response to threats made publicly by Donald Trump. In 2014, Barack Obama was president, and Obama had a very different, quieter approach.
It's not clear to me why you link North Korean threats and Daesh (Islamic State). While Daesh is an example of an organization that would like to obtain nuclear capability, they don't make a good threat. Because North Korea can't almost deliver nuclear capability to Daesh. So long as North Korea controls the missiles and nuclear weapons, they control how they are used. Once they transfer to Daesh, they lose that.
North Korea can threaten by shooting an empty missile. Or by detonating a nuclear weapon underground. But Daesh wouldn't waste a nuclear weapon that way. They aren't a threat but a danger.
There is also more danger that the United States would respond forcefully to a transfer of a nuclear weapon to Daesh. So from North Korea's perspective, a Daesh sale is more risk. It is uncontrollable. It's not very threatening until it's actually dangerous. Missile launches and public statements are better. There is less danger of a response and they are threatening without being as currently dangerous. They are potentially dangerous rather than currently dangerous.
This is not to say that North Korea transferring a nuclear weapon or technology to Daesh is not a concern. It is. But it's not a threat. Publicly saying that they're going to do so would make it more difficult to accomplish. So they won't announce it prior to transfer. Publicly saying after the transfer is dangerous--the US might respond. And offers minimal public benefit. It would make the US more frightened but not of North Korea. So they probably won't announce after transfer. That's the opposite of a threat, where the whole point is to tell the other what you will do.
Beyond all that, when Daesh was more dangerous, North Korea may have been less willing to bluster. A distracted US might be more dangerous than a focused US. If the US were already scared by Daesh, then a threat from North Korea could more easily move them to actual action. North Korea doesn't want an actual military response.
If the US were looking at Daesh instead of North Korea, then there'd be less reason for North Korea to do anything. They could talk about how the US was too busy with their own problems. They wouldn't have to create problems to prove themselves stronger, at least in domestic eyes.