In the Lavabit judgement, I saw this:
see also Agra, Gill & Duffus, Inc. v. Benson, 920 F.2d 1173, 1176 (4th Cir. 1990) ("We will not accept on appeal theories that were not raised in the district court except under unusual circumstances.").
Of course it justifies why the rule is applied for this case, but what is the original reason this rule was applied?