Authorship. When we ponder the subjective themes of human experience, it is very hard to do so in relation to the nameless anonymity of corporate creation. Thus, the strong presence of a human author is prevalent in these sorts of games -- in this context, an "author" might mean an individual or individually identified members of a small group.
The concept of authorship incorporates another feature of art more broadly: the pursuit of a particular truth irrespective of the demands of reception or sales. The sense that the artifact has something to relate and will not relent until that thing is expressed, rather than an experience to be optimized, is at work here.
A warning: don't mistake authorship for intention. There is a longstanding concept in criticism known as the intentional fallacy, which rejects the idea that a work's meaning or value is related to the creator's intention.
Player agency in games of all kinds leads to unique interpretations of play experiences; in proceduralist works, such meaning generation is stimulated by the knowledge that a specific human being set the work's processes into motion.
Artistic styles, movements, and traditions sometimes arrive via the declaration of a group of artists, as was the case with the manifestos of the early 20th century.
Indeed, The Graveyard developer Tale of Tales penned a Realtime Art Manifesto in 2006 to describe and rally interest around their style, which differs considerably from that of proceduralism: they reject rules and goals in favor of high-gloss, low-interaction 3D experiences and situations.
Tale of Tales' The Graveyard
In other cases, critics and historians describe the emergence and evolution of a style during or after the fact. Whether or not the creators mentioned above would embrace the title "proceduralist" is an open question, but such a matter need not undermine the usefulness of describing a style in the process of maturation.
As a style, proceduralism takes a stand contrary to conventional wisdom in game design. At a time when video games focus on the realistic simulation of experiences, proceduralism offers metaphorical treatments of ideas.
At a time when video games focus on player gratification, proceduralism invites player introspection. At a time when video games focus on facilitating user creativity, proceduralism lays bare the subjective truth of an individual creator.
Whether or not the style has a stable future in its own right, it issues a specific challenge to our conception of our medium from within. And that if nothing else is most certainly a feature of art.