Then what is it due to?
Do you believe that economic activity can only follow from government spending?
It could be due to a lot of things. Homes have appreciated in value and people are pulling money out of equity to buy stuff. A huge influx of foreign money into the U.S. markets. Some geek sitting in his basement wrote a computer program that anticipates market changes more efficiently.
Then again, it could be due to the new tax laws, lower interest rates, and increased free trade.
Or, it could be a combination of all those factors.