Sorry... it wasn't really a question :P
There are plenty of mounts: Erdlu,
Crodlu, Inix,
Kanks and even the mammoth-sized Mekillots, and these are used all the time by raiders,
gladiatorial chariots, or by massive trade caravans. The developers wanted to create an alien atmosphere, away from classic fantasy books, by moving away from camels, horses, lions, elephants, dogs, warthogs...
Horses are cool, and there's no real reason why that 'cannot' be on Athas - apart from figuring out how to keep them well-fed on grasses ;). But it's also nice to know that there are other cool options.