Here is why Amazon should start to sell money

Amazon is well-know to sell everything (including baby sitters now ;) So why they don't start selling money?
The idea could be a little crazy but here are the motivations:

1. They have all users' credit history so it is very easy for them to assess credit rate
2. They have all user's credit cards so it is very easy for them to assess credit rate
3. They have a huge number of transactions so they can easily move money and let user borrow 

This will be a win-win situation. Amazon can increase the number of transactions by allowing users to borrow money. Users can find very interesting rates. The whole system can benefit because the credit rate will be based on dynamically evolving parameters constantly updated

So when Amazon will become a bank?

PS: same suggestion can be applied to Ebay and Alibaba