There is a theory floating around that part of the benefit of SSRIs is that they make the user feel differently, and by feeling different it is easier to change behavior. This is independent from whether the way SSRIs make the user feel is a more adaptive state to remain in continuously over long periods. If this is true, the "therapeutic delta" would wear off as user acclimates to that SSRIs effects.
SSRIs can cause unpleasant and even dangerous withdrawal symptoms when discontinuing long-term use, so there are real benefits to minimizing overprescription.