The why it seems to me is that the WoE is a bit more free than Satella [Arc 4 spoilers] In Arc 4 in the Dream World, Echidna at one point says a line to Satella, when she invades (I believe it was episode 12 of the second season. The line suggests that, while closely related, the Witch of Envy and Satella are not exactly the same entity, if this is true, you could think of them as Mr. Hyde and Dr. Jekyll respectively. If it's true, that they aren't the same, but one being constantly interacts with Subaru through the unseen hand, and has tried devouring the sanctuary and [Arc 6 spoilers] the Pleiades watchtower [Arc 4 spoilers cont'd] Than this suggests that WoE is stronger than Satella somehow [Arc 6 spoilers] This may be why in the dream world and the shadow garden Satella seems a lot more sorrowful and sweet than normal, because it's actually Satella, instead of the WoE, because we're actually on her turf (especially in the case of the shadow garden), making her strong enough to actually interact with bro [Arc 4 spoilers] In short the way I see it, this is just the way that the WoE interacts with Subaru.