Earlier quoted context omitted.
Holding them to term is actually a bit of a joke if you think about it. The Fed is buying bonds. The government is selling them. As long as the Fed keeps buying them, the government can keep selling them. If the Fed holds them to maturity, where will the money come from to pay back the mature bonds? From the government selling even more new bonds which the Fed will have to buy. It's not a Ponzi scheme or a pyramid sc…
The fed is buying bonds on the secondary market i.e not directly bidding and taking down auctions at treasury. This may sound minute but is a huge point. See http://pragcap.com/understanding-quantitative-easing
But would the banks have all originated subprime loans had they not been able to repackage them and sell them? By selling the loans they were kept off the bank's balance sheet.
If the Fed is buying up all kinds of bonds and the banks know this, there's nothing preventing them from selling their older bonds which were purchased at a time when interest rates were higher (and thus bond prices were lower) and selling them at a profit to the Fed. They then need to do something with the money, why not buy some new bonds?
Just because the Fed isn't participating in the primary auction doesn't mean that they're not influencing the Treasury market in a huge way.