It isn't really ridable, as you can't put a saddle on it the way you can on a horse.
I admit that I personally know nothing on the subject but what I've read on the internet. But from what I read, they are ridden the same way as a horse, with a special saddle and reins. You can't use the same saddle on it as a horse, obviously.
The more I read about it, the more it seems that the Ostrich was a "missed domestication" by the ancients. It seems more broadly useful, faster and tougher. I am unsure of how well it could do as a draft animal, but lacking the breeding the horse had, there is no way to know.
I'm not so sure. Although its not a plant, mussel mollusks have some similar features. But in the region where I grew up, no one considered it edible until tourists from another region came around.
Given sufficient time, most edibles in an environment may be discovered. But that's not necessarily the case, particularly if there are cultural issues, environmental shifts, or even a sustained lack of need.
In my own area, people have fished with roughly the same methods for thousands of years. But the deep-sea fish that occasionally is caught are still considered "unfish" and not eaten despite being perfectly edible. If you can get past them looking like something from the depths of nightmare.
Which is peculiar. This is a people who made the most hideous concoctions in February, snowed in with all the appetizing bits already eaten off the animal. Lutefisk for example. What twisted and perverse imagination first thought of letting fish rot and jellify in lye, and then eat it!?
Lutefisk has been fisting our stomachs for a thousand years.
And if you will eat lutefisk, you should be up to snarfing down all sorts of boneless horrors of the abyss.
Perhaps the issue is that no-one would be fishing when those dishes were concoted out of a dizzying mix of starvation and perversity? You'd only catch unfish when you were flush with resources anyway?