Supply:
Supplied by miners. Any serious operation NEEDS to sell to pay utilities. That creates a steady supply of bitcoins offered at market price on a regular basis.
No they are introduced by miners, and supplied by miners and anyone holding Bitcoins. Supply is not a problem.
Reasons to buy.
1. Investment. Nope. Not in any real amounts. Investors like security and the bitcoin is pretty much the opposite of secure. They also like secure exchanges and the bitcoin exchanges are pretty shady compared to mainstream exchanges. That is kind of an understatement really.
Bitcoin is not intended as a get-rich-quick scheme, if it makes you money for nothing, that's great for you, if it doesn't it's not a flaw because it was never intended to.
2. To use as a transactional currency. This is the real appeal of the bitcoin. But there is no reason for someone to convert dollars to bitcoins and buy something unless it is illegal. It is inconvenient and provides zero protection against theft or fraud.
There are many reasons other than illicit goods.
They are cheaper to move. Visa and Mastercard take several percent off of each transaction that is done with them. Considering profits for most merchants is severa percent, after all expenses, eliminating Visa and Mastercard from the equation can mean saving a lot of money.