RE: WHY?
I think in large part that they just dont know what can and cannot be done. Until you start doing something - you dont know what to expect - so why not expect something incredible.
It is not till the first time you pull the trigger that you know how fast something will be/not be. Dangers, risks, skills required, etc are easily overlooked.
I feel bad at times when I try to be a reality check for new boaters - usually I will just try to steer them toward a smarter starting point (Starting with a Vee vs a Rigger etc).