IMHO a very sensible decision. Lowering the speed limits on these two roads would be expensive and intrusive due to all the 50mph repeater signs but more importantly it would have no effect on the casualty rates.
As you have local knowledge, I will take your word for it, but I am generally in favour of lower limits on rural roads.
My disappointment comment was based on local experience of a road with a bad crash record where the limit was reduced. The vast majority of users obey the new limit and they have the effect of a rolling road block on the would be racers. The slower average speed has dramatically reduced the number of close passes of cyclists as drivers used to squeeze through in the face of oncoming traffic, now they seem happier to hold back.
Although the limit was reduced in order to deter boy racers from killing themselves, it has had the effect of reducing the danger caused by these drivers who treat speed limits as speed targets and so create a hazard for cyclists and pedestrians.
The new 50mph signage could not by any stretch of the imagination be described as intrusive.