The simplest explanation is, in the absence of any evidence to the contrary, the most likely. And here clearly the simplest explanation is that the results for customers could have been better if there were more planning resources, or the resources were under less pressure. This is what I was saying, and you note that I was careful in my post to point out that nobody was deserving of a criticism for their work on the matter.Knowing many of the team in Chiltern Railways train planning, I would say this is most unlikely. It may have been that there were no spare units available, having been used to strengthen services / run additional trains on other routes, who knows. I'm sure there was a much better explanation than 'nobody thought of it'.
I also note Chiltern didn't even attempt to run a bus, even though only one bus and driver would have been required. That strongly implies simply not having the planning capacity to deal with it, rather than that there was a plan to run the service but no unit was available, or some other technical constraint.