I have seen gouges/ruts in Olfa mats, too. (Like at a LQS when the same lines are used over and over.)
It does help to change where one cuts on the mat to attempt to get more even wear on a mat.
It also helps to use a sharp blade that requires little pressure to cut as compared to using a dull blade and heavy pressure to prolong mat life.
It is not reasonable to expect a mat to last forever if it is used a lot.
PS: The edges on rulers can also become worn down with a lot of use. Then one gets a curved cut instead of a straight cut. This become noticeable when one is cutting strips. You know the fabric did not move - and you notice that the cut edge is not lining up nicely on a line when you move the ruler. I finally become aware of this "erosion" when I had worn down almost an eighth of an inch in the middle of a ruler. (blush)