What made the building business turn around so fast?

WASHINGTON (AP) — The U.S. housing market has given a sudden jolt to what appeared to be a slumping economy.
Builders broke ground on homes last month at the fastest pace in more than seven years. The stepped-up construction is helping boost sales at stores like Home Depot and Lowe's and improving the likelihood that the U.S. economy will accelerate after likely shrinking early this year."

Last month they were pessimistic, now they are optimistic what caused it?

When we remember we are all mad, the mysteries disappear and life stands explained. Mark Twain.