Engine maintenance

Engines seem to have become a machine that is supposed to work, independent of the damages this machine has suffered. Any machine has to be maintained in order to work and function properly, meaning without explosions of sudden shut downs (only some examples).
But this is not the only consideration that has to be made concerning the cars maintenance, the other which might be even more important is the which concerns one's environment which suffers under the badly maintained engine. The greatest problem of the not well maintained engine is the oil leak something that for one can cause severe damage to the machine due to insufficient cooling or lubrication, the second problem which is even greater is the effect the oil has on the water and environment after having left the car or boat. (Most engines use water as main coolant)
The oil having left the car engine often enters the freshwater supply something that impacts on the health of every life-form drinking from that countermanding water supply. Boats 'only' destroy sealife something that is considered less important by most sailors as it appears, but the truth is that the ocean life and the streams in the ocean affect the every region of the planet.
Why is it that many people either don't care or justify the cost to the environment with too great expanses caused by good maintenance. (In my opinion someone who is not able to affort the maintenance of an engine should not use one.)