Zebras are equids, similar to horses. Some have been trained for riding. I think the reason it doesn't happen more frequently is because they are wild. They aren't domesticated in the least.
Sort of like a bobcat or lynx is just a large cat, why don't more of us have them as house pets or in our barns as mousers. Some people do have bobcats, but they are not domesticated.
Horses that are wild are captured and trained. Neighbor in Tenn. took in wild horses rounded up by the states in the south west. Wild running horses, even wild camels were sent to farms free of charge, only problem was the specifications on height and kind of fence, amount of acreage, watering points and shelter were a big money zapper.
I just happend to be visiting their farm/ranch when one wild stallion was brought in, this horse was all mussel, almost looked starving, not an ounce of fat on him. Probably the most magnificent horse I have ever seen. Totally wild, coat gleamed, terrified of people, and one nasty horse to mess with.
So strange, when turned loose in the field with the gelding ride on horses the tame horses looked like blimps beside him. Big fat over fed and no way as healthy as he.
About 9 months later the neighbors wife road up on that stallion with complete control. Not something I would advise as 15 miles away a mare goes into heat and the stallion goes crazy.
So now I got to thinking that if female Zebras were raised about either geldings or mares, would they not emulate their actions, would they not come to think they were in fact horses ????
Is it possible to find a mare that lost a foal and give her a new born Zebra, will she let it feed ??? Will the new born follow the direction's of and training of it's mother???
Genetics vrs upbringing, if one follows this path for 5-6 or so generations can the Zebras now be tamed???