My guess is that they don't want dodgy trail work that they can't sign off on in their land. Perhaps.1. Cutting down trees, dislodging rocks is destroying landscape not regenerating it.
2. When I was there the DELWP workers said that those particular trails are going to be rebuilt (don't know by who), next year. So why would you completely destroy a trail that and then as you say "regenerate it" for a year then allow trails to be built there after that. Seems completely illogical.
In any case. Pv/delwp are delwp happy to support trail making and riding when the process is done properly - look at lysty and youeys. Don't be so against them when you're only speculating