private mortgages

Why would anyone invest in Tbills at 0% when they can provide a private mortgage and earn as much as 8% fixed rate return?
I am a Realtor and a real estate investor in Lakeland Florida. I find bank owned deals weekly that I can pick up for 40 to 60% of current market value if I have the funds available.
Think about it if you provide a private mortgage to someone who buys right you are earning a very good rate of return plus it is protected by a first mortgage on one single property, a promissory note, title insurance, and hazard insurance, and it will be at most a 60% LTV loan.
This is also a win/win scenario because if I buy a house using a private mortgage at a huge discount then I can resell the property at less than market value with a wrap around mortgage to someone who may not be able to get funded during this credit crunch.
Everyone wins! The bank gets it off their books, I make a profit, the private lender makes a good return on investment, the end buyer is able to buy instead of being forced to rent. And the market improves because there are less houses on the market dragging down prices.
The funds are all handle professionally through a title company as if the funds were coming from any other lender.
Where else can you get returns like this with this much protection?