Because of a similar reasoning why gas station owners don't get complicit in crimes when they sell fuel to potential criminals. At least as long as they can plausibly deny knowing of the crime and they provide similar service than to any other customer.

Wikipedia, and the sources where its content comes from, is not intended to help anybody specific. Flying to North Korea and holding a lecture there is firmly beyond the line where the US government starts to care because it demonstrates clear intent. Especially since during the Q&A and other activities other information not available to the public could have been discussed. And even if there was no secret sauce involved, an expert's opinion can still save the North Koreans a lot of time and money when pursuing their goals.