"Ride a bike", for every vehicle the word 'drive' is used.For example drive car, drive a bus etc.But for a particular vehicle 'bike' why is the word drive not used,and instead of drive the word ride is used in sentences.
"Drive" seems to be idiomatic for most motorized vehicles, while ride is idiomatic for unpowered or self-powered vehicles. As you say, you "drive" a car, bus, train, boat, motorcycle, scooter, truck, tractor, carriage, taxi, limousine, or hearse ... but you "ride" a bicycle, tricycle, unicycle, skateboard, toboggan, or surfboard.
You also ride a horse, camel, elephant, donkey, pony, mule, yak, ox, reindeer, ostrich, or any other animal that can be ridden.
There is at least one exception: Because a hoverboard is so much like a skateboard, most people seem to prefer "ride" for this, even though it has an electric motor. In the same way small electric scooters are "ridden" -- unless you sit down on them, in which case either "ride" or "drive" might be fine.