Matt Dupuis blogs at FP Watch and currently also at World Politics Review.

About North Korea's decision to kick out IAEA inspectors and to restart its nuclear programs he asks:

What is Motivating Pyongyang This Week?:

I'm speculating, but maybe North Korea knew its launch would prompt the US to turn to the UNSC for retaliatory action, which it could then use as a pretext
to jettison the Six-Party Talks and related accords it was no longer
interested in adhering to. If that's the case, it raises larger
questions about Pyongyang's motivations, specifically why
they have periodically agreed to cap or halt illicit weapons programs
(as it did under the 1994 Agreed Framework, the moratorium on ballistic
missiles in the late 1990s, and the more recent accords under the
Six-Party Talks) but later reversed course so defiantly. (bold added)

Simple questions, deserve simple answers: North Korea believe in Pacta sunt servanda, the U.S. does not.

North Korea needs primary energy, i.e. oil, and is willing to make deals to get some. It sticks to such deals but only as long as the other party adheres to those too.

In all three examples given in Dupuis question it was NOT North Korea  that "later reversed course so defiantly" but the U.S. that broke spirit and letter of the deals it had made.

1. Agreed framework:

The objective of the agreement was the freezing and replacement of North Korea's indigenous nuclear power plant program with more nuclear proliferation resistant light water reactor power plants, North Korea promised to included oil shipments from the U.S.

The oil shipments were late, the replacement reactor the U.S. had promised was never build and trade sanctions that should have been lifted were kept in place. As the U.S. showed no intention to seriously stick to the deal, North Korea walked away from it.

2. Moratorium on ballistic missiles:

• Sept. 13, 1999: North pledges to freeze long-range missile tests.
• Sept. 17, 1999: President Bill Clinton agrees to first major easing of economic sanctions against North Korea since Korean War's end in 1953.
• June 2001: North Korea warns it will reconsider missile test moratorium if Washington doesn't resume contacts aimed at normalizing relations.
• July 2001: U.S. State Department reports North Korea is developing long-range missile.

Again a. North Korea made a deal with the U.S., b. the U.S. did not stick to that deal, c. North Korea stopped doing its part.

3. Six Party Talks:

Five rounds of talks from 2003 to 2007 produced little net progress until the third phase of the fifth round of talks, when North Korea agreed to shut down its nuclear facilities in exchange for fuel aid and steps towards the normalization of relations with the United States and Japan.

Steps towards normalization by the U.S. were not taken. The fuel aid was stopped in December 2008 as 'response' by the U.S. to North Korea not accepting additional conditions the U.S. tried to add unilaterally:

North Korea has complained that the United States has not made good on its promise to remove North Korea from a list of state sponsors of terrorism, as President Bush announced in June that he was prepared to do, and instead has made new demands. One of those would require North Korea to accept a strict and intrusive verification system before the United States would carry out reciprocal steps.

As many other countries North Korea had hoped for that a new Democratic U.S. president and congress would take a different course than the ever deal-breaking Republicans. The recent legally unjustified issue of a U.S. instigated letter by the UN Security Council president on a NoKo 'satellite launch' has made it clear to them that there is no change in U.S. policies. Unless those change there is then obviously no point for it to continue talks over deals the U.S. obviously does not intend to follow through.

Dupuis' question is quite typical for general U.S. public views of foreign policy issues: very one-sided and blind towards its own faults.

But there is a serious defect in U.S. foreign policy when people who work in that field believe their own side's propaganda instead of obtaining a realistic reading which necessarily must include facts and some understanding of the viewpoint of the other side.