Hmm, I’ve seen maybe a handful of two-way streets change to one-way over my entire life, and have never seen a one-way street change direction. If ~1% of streets changed direction every year, there’d be mass confusion and frustration.
One major thoroughfare in London changed (if I remember right) from one-way in one direction, to one-way in the other direction, to two-way, in the space of a couple of years.
People got used to it very quickly, to the extent that they would not remember the change ever happened.
If you have a broad enough roads to have two-way streets everywhere, there's little motivation for it to change. [Edited to note: at the level of individual cities, OSM's directionality was often estimated to be 100% correct]
But, with some narrower one-way streets, there becomes a clear motivation to tweak things to improve traffic flows (and also tweak the surrounding two-way streets).
There’s apparently a trend of converting one-way streets to two-way; cities have realized that one-way streets are a little too efficient, they increase bandwidth but often cities want you to stop and shop.
Indianapolis has been moving that direction, at least, but I don’t know how widespread it is.
Im yet to read TFA, but I could foresee there being plenty of one-way private drives and parking lots - if not included in the study, I tend to agree with you