Here's why:

* Linear refers to a straight line or a measurement along a straight line.

* Centimeters are a unit of length, which inherently measures distance in a linear fashion.

Therefore, saying "linear centimeters" is redundant, like saying "straight straight line" or "round circle."

When talking about length, we simply use the unit "centimeters" (cm).

For example, a pencil might be 15 centimeters long, or a table might be 120 centimeters wide.