This article from Animalz is relevant: https://www.animalz.co/blog/vertical-volatility/
I've been talking about open and closed systems a bit here. I'm doing my normal thing: cowpathing my way to clarity on a topic, or at least stability in the terms I use to discuss it.
With the topic of specialization/positioning, we have this pretty well-established model and terminology we use to discuss it:
The actual experience of specializing, viewed over years/decades, is partially defined by the specialization approach (vertical, horizontal, etc.) but it's also heavily defined by the fundamental force of commoditization and the nature of the system that you specialize in.
This article from Animalz is relevant here because they are describing the effects of open/closed systems on keyword churn/stability. As you read it, when they talk about "volatile verticals", think of those as an open system: ones with little centralized control and high levels of chaos, novelty, and flow.
If consulting is helping clients initiate or respond to change, then systems with lots of change are going to have lots of opportunities for consultants.