I wrote a post a while ago on this. Rather than rewriting it, I'll just reference Eichengreen's summary paper targeted at a relatively general audience:
http://www.nber.org/papers/w6060.pdf
Quote:
There now prevails a remarkable degree of consensus among specialists about the causes of the Great Depression. Recent scholarship has resulted in striking agreement on the reasons for the crisis; the modern literature can be regarded as having substantially solved the riddle of the Great Depression. That literature focuses on the gold standard as the mechanism that turned an ordinary business downturn into the Great Depression. The constraints of the gold-standard system hamstrung countries as they struggled to adapt during the 1920s to changes in the world economy. And the ideology, mentalité and rhetoric of the gold standard led policy makers to take actions that only accentuated economic distress in the 1930s. Central bankers continued to kick the world economy while it was down until it lost consciousness.
The crash of 29 led to changes in international trade laws that had the intent of protecting domestic markets, but had the effect of freezing international trade.
One interpretation of events also lay the blame on the gold standard. if the government could jump start the economy by printing money people would go back to work and real wealth would be created. Another perspective is that the whole problem was too much easy credit, creating a vast bubble that just popped one day; that invented wealth of any sort just creates bubbles..
Another cause is the agricultural side of things. the US greatly increased it's agricultural production during world war 1, afterwards the market was more competitive and farmers faced lower prices at market; by the time of the 29 crash many farmers were reliant on farm loans to get by; when the banks began failing many farmers found their lifestyles had become uneconomical.
TO address your question directly
workers still wanted to work, bosses still wanted to run their businesses, and bankers still wanted to make money. So what happened?
people had no money to buy anything, so all the will to work in the world just resulted in overflowing storerooms and failed businesses.
Crossposted to /r/askeconomists: http://www.reddit.com/r/askeconomists/comments/34o6p8/xpost_from_raskhistorians_why_did_the_great/