You are probably thinking: because we have to.

Too often, cleaning the cleanroom to a particular standard becomes an end in itself; reaching the goal or staying within limits of contamination may not be adequate. The ultimate goals—assuring cleanliness and quality performance of the product—are lost. We have to meet or exceed the requirements. In cleaning the cleanroom and the product, our goal should be to clean critically, to adopt value added cleaning. By the way, our view of critical cleaning is that it is a lynch-pin process, one that is essential to product quality. Therefore, critical cleaning may occur not only in the cleanroom but also very early in the fabrication and assembly process.

Teaching employees to adhere to rules of behavior or to a specific cleaning protocol is necessary. However, for both product and cleanrooms, there is no substitute for understanding the “why” of the cleaning process. Education is important whether your product and cleanrooms are cleaned inhouse or are outsourced. In fact, when you outsource, educating the employees of the contractor may be even more important.
From: Point of View: Why Clean the Cleanroom?