CJ,
Same reason that it's time to sell stocks when Business Week or someone else announces it's a BULL MARKET...it's usually at the peak of the market.
It's likely rates will continue up after a small pullback of the breakout. If you are in an ARM, and millions of folks are, it's gonna be a bad thing. As more and more household income goes into making the mortgage payment, there will be less and less for other expenditures.
Also, generally speaking, rising rates on fixed investments draws money away from the stock market and you know what that means.