So you think it's only retailers that don't wish to sell Hull Trains and Grand Central advances in the extended booking horizons that don't sell them?
Interesting. I had the distinct impression that the forum's site was unable to offer them, but I can't comment on that with any authority.
It is those other sites that only sell fully flexible tickets, but don't then allow reservations, that worry me more. For example, friends booking for travel with family before the main horizon being sold full fare tickets, without reservations, and believing (in their naivety) that this must be the best possible price.
The LNER practice is sharp, but is at least balanced with getting what you think you're paying for.