Here's why:

* Acceleration is the rate of change of velocity. It's how quickly an object's speed and/or direction changes.

* Velocity is speed in a specific direction.

* Higher speed means the object is already moving fast.

To make a significant change in speed (either increasing or decreasing) from a high speed, you need a greater force applied over a certain time. This translates to higher acceleration.

Example:

Imagine you're driving a car. To accelerate from 0 to 30 mph, you need a certain amount of force from the engine. To accelerate from 60 to 90 mph, you'll need more force, and therefore a higher rate of acceleration.

Important Note: This doesn't mean that an object can't accelerate at high speeds. It just means that it will take more acceleration to achieve the same change in speed compared to lower speeds.