Pearlsasinger
Up in the clouds
I think it is one of THE most importnat things a horse should be able to do. Like the OP, I don't recall having any horses that couldn't or wouldn;t hack alone, you just expected a horse to do it.
It seems to be a very recent thing andf I don't know why - maybe when people learn to ride these days, due to certain trends and maybe H&S/Insurance, riding schools do more lessons in schools as opposed to lessons out on an hours hack? That is what we used to do at the riding school - they didn't have fancy arenas back then your lessons were just in the fields. If those fields were too wet you'd go out on a hack instead andm, to be honest I think this is where you learn to RIDE.
People now seem very nervous of hacking out and maybe too many yards have been set up without thought for actual availability of decent hacking (ie, too many busy roads nearby) so people don't venture out and then the horses don't get that vital experience. It's really sad that some people don't see the importance of hacking out and think schooling a horse and achieving an 'outline' is the basis of riding.
I could have written that myself, and you're much younger than me, LadyT25.
I am often horrified by some of the practices I see when others are hacking, they really seem to have no idea at all. We were taught to thank drivers who passed wide/carefully/slowly, to trot on to a suitable passing place if necessary and to ALWAYS be aware of other road users/pedestrians. We were also taught to ride with care off road, not knocking over dog-walkers/cyclists etc and to keep a sensible distance away from other horses and, one of my personal bugbears; not to let our horses 'talk' to others over walls.