I imagine that it was overhunted because it tasted so good, because from what I understand it was a pretty stupid bird and wouldn't be too difficult to hunt, making it a poor trophy
Additional question: Is there any evidence that it was actually particularly stupid? As far as I can tell, people conclude this because it was hunted to extinction so quickly, but I don't think stupidity is required to explain how this could happen to a flightless bird found on only one island.
Add on: Are there any commonly used recipes specific to the Dodo?
Not sure if this is allowed under the rules of the sub but there was an interesting documentary regarding all of the myths surrounding the Dodo on BBC Radio 4 today, including a report of the recent sale of the only privately owned complete skeleton.
Here is the link to a download, UK only I'm afraid: http://www.bbc.co.uk/programmes/p055fw8k