Is there any research on this news impacting voter participation? Ie if they feel their party is losing do they throw in the towel even though they still might have had a chance?
Sure, it won't impact the election in that state because it's polls are closed. But in theory it could affect the election on the west coast were polls are still open.
As to why so early, they have enough confidence in exit polls and other previous polls to say that, for example, Hillary is not going to win Oklahoma.