Why might the recession of 2008 not have brought about the degree of extremism triggered by the depression of the 1930s?

The most likely reason is that by the time of the 2008 recession, people, word leaders, and world organizations alike, were aware of the dramatic consequences that the extremism of the 1930s had not only on the economic, but also on the social and geopolitical landscape. For this reason, most people tried to act differently, in order to avoid the same dire situations of the past (mainly World War II).

Another reason is that the Great Recession of 2008 was not as dire as the Great Depression. In both the economy did plunge a lot, but in the Great Depression the fall of economic activity was much more pronounced, and lasted for a lot longer.