I suspect that the issue is that some pedestrian footways are not connected to the rest of the network.
If you take a look for example at the junction of North Drive and County Avenue, the only route for a pedestrian is around the back of a recycling/ cycle shed. Presumably though the pedestrians can cross straight across the entrance of County Avenue.
Presumably something like https://wiki.openstreetmap.org/wiki/Tag:crossing%3Dunmarked and the associated tags would need to be added across the entrance of this junction, and others