What is the cause of tire marks at the extreme ends of runways?
The marks are left by the tires of landing planes when they touch down -- that is, ordinary routine landings.

The wheels of a landing aircraft do not start rotating before they hit the runway -- so right at the moment of touchdown, the wheels will at first skid along the runway surface until the friction between tires and runway has delivered enough angular momentum to the tire to spin it up so it matches the ground speed of the landing plane. Once that happens, the wheel will roll normally.

This skidding causes the skid marks you have observed.

Even if the runway is usually used in the east-to-west direction, there are still enough days where landings are from the west that both ends of the runway will collect tire marks. How many days that are doesn't really influence how black the runway gets, only how long it can go between having the rubber buildup cleaned off.

At the few airports that are really only used in one direction (such as the famous Princess Juliana Intl Airport at St. Maarten, which does not even have charted approaches from the east due to terrain obstacles) you will find the tire marks only at the touchdown end of the runway.