It's two different groups. First you have foreign groups/investors that are parking money in real estate in the US since it keeps their local taxes low.
Then there's groups like Zillow b4 they gave it up that are buying up real estate to sell as well.
The investment portion is mostly concentrated in the cities. We have whole buildings in NYC that are close to empty because many of the apartments were bought up by foreign investors.
Is gotten so bad that Canada is banning foreign investment in real estate to slow down their housing market.
Canada's budget also includes billions for new housing and measures to help Canadians trying to get into the market.
www.npr.org