I have found at the companies I have worked for it is two things for a layoff: cutting a product/change in strategy and how much you are being paid. Layoffs for performance tend to be more one off than a massive cut.

What I am most surprised about is how many really good performers get cut for a product or strategy change. A company will be cutting a high performer while searching for a high performer at the same time like it is taboo to move people within the company.