right. Personaly, I think 3 things came into account:
- there is hype and stories, and miners are scarce. If they are scarce, in people minds it means that there is something to get.
- the math are hard to get. Sorry but explain how works a decrease in value overtime is not linear but exponential :-), some people don't catch it really. I had to take 10 minutes to explain that to a colleague.
- and when you type "bitcoin calculator" on google, you arrived for example on a BFL sponsored page that fools you (http://www.bitcoinx.com/profit/): sure there is a profitability decline per year on their calculator, but check the value. If (for example) you enter the price of the cointerra and its hashate, the site let you imagine you will make a profit.

Personaly until I used the "expert mode" with http://www.coinish.com/calc/ I didn't know where to get a good simple calculator.

So people are guided on wrong information and (a bit) greed and hype.