I’m pretty sure that IMBA is staffed and run by volunteers so it’s a bit churlish to complain that they’re not doing enough.
I haven’t received their newsletter for a while but every time it came round there would be a story about access rights, either highlighting a problem, appealing for assistance, or reporting on an attempt to reclassify a right of way (which is an expensive and thankless task).
I also think the comparison with CTC is unfair as when IMBA UK was set up, CTC did hardly any advocacy and concentrated on member services instead, so it seems IMBA did their bit in bringing attention to the issues in the first place.