I'm not surprised. From a British POV it was a relatively minor part of a much larger conflict that Britain was done with when Napoleon defeated, and Denmark-Norway was for most practical purposes treated as "just" Denmark, since Denmark was the more powerful part of the union by far.

From the Danish and Norwegian side, Britain annihilated or captured most of the Danish-Norwegian fleet because Britain expected Denmark-Norway to enter the war on Napoleons side (as a consequence, Denmark-Norway of course entered, but severely weakened), and Norway was blockaded and faced famine from 1808-1814.

After the war ended, the Norwegian mainland was handed over to Sweden (Iceland and Greenland were also Norwegian at that point, but stayed with Denmark), but Norway took advantage of the process and passed a constitution and briefly went to war against Sweden to force a better settlement, resulting in a relatively loose union. So this whole affair had a very significant effect on the formation of the Norwegian state.