I think it's perhaps because the paths on the ground are concessionary rather than actual rights of way. As such, they probably can't be marked on the OS map as the concession could be withdrawn at any time, or may not apply every day of the year - in theory, if not in practice.
From your description, you were at Lud's Church but it can get exceptionally muddy down there (as you would expect). The paths beyond it can also get very sticky as well - but are worth persevering with as the ridge above is glorious.
Staffs Wildlife Trust have taken over management of the Roaches Estate on a 125 year lease. I'm not 100% sure of the boundaries but it may be that the paths will be "improved" in due course. But it's the countryside - am not entirely sure what you can do to prevent mud!