I think that’s part of the problem. Some of these paths are walked by dozens or hundreds of people every day, but it can be years between visits by active mappers who care about making sure there’s a correct sac_scale tag on the path. We now have a map layer on osm.org that shows sac_scale, and SCEE supports tagging it, but it’s still niche. Most actual users of the data (the users of hiking apps like Komoot, Alltrails, Outdooractive) don’t know what OSM is or that it would be really valuable if they contributed to it.
It’s worse in some regions of the world than others. It would be an interesting data analysis to look at the coverage of the sac_scale tag, i.e. what percentage of paths that probably should have the tag actually have it, and identify priority paths for surveying.