Why did horses die out in North America?

https://www.horsetalk.co.nz/2012/11/29/why-did-horses-die-out-in-north-america/ [horsetalk co nz]

Recently, I’ve seen a couple of posts where someone felt the need to assert that Native Americans were riding horses when the Spaniards arrived. They were not—horses in the Americas had died out thousands of years earlier.