Who the hell finds it fun to either waste time trying to lure them into a trap or chase them down? And it’s so much worse against ai because they don’t need to micro manage the way humans have to so it seems whenever I use them they get wrecked under the first half assed volly from any unit. This applies to literally any game. Who has fun with this shit?
Also because they were absurdly expensive for the civilizations that were using them. The loss of their chariots to Sea People invasions and the cost of replacing them is sometimes listed among the reasons for the Bronze Age collapse of the Hittites and the decline of Egypt despite their battlefield victories.
And it takes a lot of time to train soldiers to effectively ride horses, shoot bows and especially to ride horses while shooting bows while also making sure there’s enough money/logistics to take care of those troops. Much easier to give tons of people a simple bow and tell them to have at it. Or spears. Just… spears for everyone.