hi! I collected these links on the use/decline of chariots in warfare for another post the other day; they may be of interest to you. The tl;dr is that the horses at that place/time were too small - do take a look at some of the images in the posts.

use in warfare

• How were chariots used in Bronze Age warfare?

• How could chariots be used militarily?

• Why were chariots so effective in ancient warfare?

• How did chariot battle tactics differ between the middle-eastern nations (say, at the height of the Persian Empire) and those of the British isles (say, during the Roman invasion)? How were they similar?

decline

• Were chariots ever used by European powers? If not, when and why did the chariot stop being used in combat?

• Why did chariot usage decline?

• When did war chariots stop being used ?

• Why did people stop using chariots in warfare?

same question but for the British.

A lot of it is to do with breeding. Horses were not strong enough to carry a man in battle, and were only able to pull chariots. Over time horses became stronger through selected breeding, and by the first millennium BC they could be used as actual cavalry. From then chariots gradually fade out of warfare, being more expensive and not as effective as simple cavalry.