re: "American corporations are ALREADY sitting on trillions in underinvested cash."
A huge amount of that is overseas - where, if the money is brought back to the U.S., it will be heavily taxed. A stupid law keeps corporations from bringing their money - already taxed once - home.
re: "why are they not doing that now?"
Because they think things will be even cheaper later, would be my guess.

Gold is $1,581/oz today. When it hits $2,000, it will be up 26.5%. Let's see how long that takes. - De 3/11/2013 - ANSWER: 7 Years, 5 Months