[Advaita-l] Previous Kali Yugas in Shastras?

[Kalyan]

// an innumerous amount of Kalki avataras
that have already descended, yet we have no stories about them.//


On a related note - why are horses and chariots mentioned in the vedas, but there is no mention of cars, buses and trains? 

Why does kalki have to come on a horse and carry a sword in kali yuga when he could have used a tank and a gun?


Regards
Kalyan