Think of it the other way around - to field cavalry, you need horses too. Here's some previous threads for your perusal on the decline of the chariot:

• u/JoshoBrouwers has an overview of chariot combat in general, which also deals with their fall at the end;
• and u/PM_ME_UR_SADDLEBREDS looks at the reasons for the rise and fall of the chariot.

Of course, if anyone else would like to take on the question, please don't let this linkdrop stop you! More can always be said, and if it's good, you might end up being part of later linkdrops!