I thought Blizzard said a while back that most players will quit after Normal? So…rather than letting everyone play around with rank 1 runes and at least see the various effects you aren’t going to let them see them at all?
Totally! Reward for more invested players, and very likely a way to entice players not to just stop at Normal.
To be honest the repetitive difficulty levels in Diablo games is not a very straightforward mechanic. Plenty of games have difficulty levels, but there are only a handful that use them as progression. If we can communicate the intent of the game to people by showing unlocks in future difficulty levels, maybe we can get more people to play beyond Normal.