Thanks to everyone who replied to my original posting.
It's clear from the OS website
https://www.ordnancesurvey.co.uk/blog/2011/07/how-often-do-we-update-our-paper-maps/ that updating of paper maps depends very much on commercial factors, in particular the popularity of particular sheets and their existing stocks of any sheet.
The OS is a business for which walkers are presumably only a small part of its market, given the extent of marketing digital products to commercial land and property owners
I think we can all agree that the OS mapping subscription service is excellent and is very good value. I plan all my walks on it and then mark up my paper map with the route (or print a copy). I don't rely on smartphone maps, but carry one as a backup.
The criticisms of the currency of paper maps, such as forests and deforestation, and the lack of fence boundaries now that walls are no longer being built in mountain and moorland areas, are, I suppose, something we have to live with.
On the issue of priorities for mapping I think that the footpaths on the ground (dotted lines) could be more prominent than the green-dashed ROWs, but I don't suppose there's any hope of making changes to long established graphics.
Dave