This is not so much specific to REST (although very common), it is more in the realm of TBL's "Cool URIs don't change" about URI design [1].
Even though the actual call to the REST service is opaque there is always a person that creates the calling application. Design an API that you would like/enjoy developing against.
What a strawman. Just because URI layout is orthogonal to REST does not make it a non-concern to REST proponents. It has nothing to do with REST. It is a good practice. Both are true.
It's only confusing if you think REST nebulously means merely "good web API design" or "good usage of HTTP."
The canonical example is the "collection" URI,
And the "element" URI, Would anybody balk if all my REST API's URIs where obscure hashes?So my collection is now,
And the element is, Is this no worse or better?