Not everything, there is branding values too. Manufacturers don't see thrashing a fossil fuel car in a reckless way as their brand. Except Toyota GR and Hyundai N. Fine in Asia obviously but not Europe.
I'm not sure this is valid, they have no problem going to the Dakar and WRC2... I think it's more to due with the WRC not being a good return for the costs.
Other than the Roger Albert dont think any current UK forestry events could remotely get anywhere near the required mileage and as you say nil possibility of anything new appearing on the scene woods...
Recce interviews: https://youtu.be/IzYGTgjw7Pc?si=YDh9InQGsyZjEVfX
[WRC] FORUM8 Rally Japan 2025