Think of the process you undergo when you write e-mail for instance. You write something, which you intend to express your thought. The act of writing brings the realization "No, this is not quite what I wanted to say". So you revise and alter. But after a number of drafts the pressure mounts : "OK, enough dithering, this is what I wanted to say". You have lost track of the inarticulate thought under all the expression, so you no longer want to revise or change the expressed thought.
It is the same with "process" : while not written down (inarticulate) it can not be tested, verified, probed for correctness or fitness to purpose. I believe that this is the underlying reason people declare themselves "against process" - they anticipate and fear the unending journey of self-examination that articulation leads to.
As soon as the process is written down - articulated - it becomes false to fact, false to what we really do. And it becomes the crux of a complex balancing act of forces : - the energy invested in articulation drives us to say "This is good enough, accept it as written (with some exceptions)" - the mismatch between articulation and reality drives us to say "This is false and needs revision (to account for exceptions)" - the emerging elegance of our articulation drives us to say "This is true and nothing else exists (no exceptions)".
Also, if we feel more comfortable in the act of articulation than in performing the work itself, we may want to keep articulating for much longer than is reasonable, and eventually get disconnected from reality; we anticipate and fear the pain of confronting our articulation with reality. I think this is the trap that the "defined process" people fall into.
At some point the cycle begins anew - you find yourself doing or thinking something that requires articulation again, because you feel (inarticulately) that it is quite unlike what you have articulated so far.