The short answer is the "Mises Caucus" happened.
The history is long and the details are mind numbingly arcane but what is easily verifiable is that members of the Mises Caucus, deliberately and in a nationally coordinated effort, systematically took control of several state affiliates of the National Libertarian Party, used their delegates to remove language from the platform condemning bigotry and supporting reproductive choice on the grounds of personal privacy.
Their justifications vary, with the official story being the desire to welcome a more diverse subset of the "Greater Liberty Movement" (it's a recurring phrase) into the LP that had previously been alienated by these two aspects of the party's platform, but were still "libertarian" according to their definition of the word.
In reality though, several members of the MC through their extensively documented conduct online through various social media channels, as well as through their behavior in person where physical conflicts were not unheard of, they have shown themselves to be tolerant of distinctly un-libertarian patterns of belief that were increasingly prevalent in Libertarian Party spaces and have since ultimately become the predominant vibe. Delaware was not immune.
We did our best to hold them back in the best way that we knew how once the threat was apparent, but it was too little too late and the ballot qualified Libertarian Party in Delaware, as well as the recognized National Affiliate, is now a Mises Caucus social club.
So we voted with our feet and left.
Again, the details are tedious but ultimately irrelevant. We maintained control over certain assets, they gained control over others, we may some day figure out who was right and who was wrong but in the meantime there are more important things to fight and the Libertarian Party infrastructure has never been a necessary component of our political activism and was often a detriment instead anyway.
Non-Partisan Delaware is constituted of most of the same people with most of the same capabilities as the Libertarian Party of Delaware you may have come to know up through ~2018-2020 or so, but we are trying something new to break from the Libertarian Party's extensive record of underwhelming progress and the direction being taken by its current leadership.
This organization does, however, still exist independently of the Mises organization in Delaware, and we have not surrendered any claims to our rightful status as the Delaware National Affiliate or the regularly organized and constituted governing authority of the Delaware Libertarian ballot line. We just have better things to do than press those claims at this time.