Now it's an interesting question that improvements can be permanent while spikes are temporary.
@Paulmanlike's correct, tinnitus is very much an inexact science. However, medicine is full of such asymmetries. The body strives for homeostasis. Torn skin, broken bones, grief, or hangover, are all temporary states, and the body eventually returns to baseline. Why couldn't a tinnitus treatment have an asymmetry just like this, where healthy, beneficial states are permanent, while adverse states are usually temporary? I don't think anyone in the world knows - but there's a LOT of precedent for it in other fields.