They are either unaware of the evidence or are willingly ignorant and ignore it. The horse has not evolved. And here's the evidence. This among other false examples were used to show how the horse progressed in size, and decreased in toes. But they are arranged in textbooks in such a way that you would believe they were.
Evolutionists believe that the smaller horses evolved into the bigger ones.
Not only this, but sometimes 2 of the alleged progressive forms were buried together. But in truth, the number of ribs fluctuate between the species. Not progress or regress. They say this is the first of the 3 toed horses. That is until cryptozoologists found one still alive in 1903.