My take is that the DPRK has wanted to normalize relations with the rest of the world ever since the Korean War ended, but their hard line stance on reunification was and remains a stumbling block on establishing a proper peace treaty and changing those relations. Previously that's a price they've simply paid - but now they have two factors that I can see that are pushing them to try something new. The first one is the post-COVID economic crash: the DPRK's economy was slow to grow already and the loss of what trade they had with China and Russia made things worse, so opening up relations with other countries looks more valuable than it did before.

The second is America's slipping hegemony: the DPRK's economy would be massively boosted if they could get some of that Belt and Road investment, become a member of BRICs, trade with China using their own currency, or any of the other things that have become possible in the past couple of years in the international community, but as long as they can't get over that first hurdle of signing a peace deal with the South those doors will remain closed to them.

I'm sure there are internal factors too. The media portrays the Kim family as though they're the sole directors of policy in the country but they've got a head of government and a head of state and factions within the worker's party and all of those other things that other countries have to deal with. It could be that COVID was just the last straw and now there is a demand within the WPK to try something different, and this is the result - but without reliable reporting on the DPRK's internal politics this is all speculation on my part.