One possibility, which I don't believe, would be that Apple has too big inventory of 8gb models and they want to sell them away before new model and/or 4gb is almost out and they don't want to make another batch of the old model.
Anyway, not being able to drive normal tv as a screen (4k@60Hz) in 2016 is a deal breaker to me. Waiting for June...
But 8GB were BTO ....somehow I don't think they had a huge stock they needed to get rid of.