This is particularly crucial in positions that aren't easy to fill. If your corporate ownership structure changes, your temporary permit could become invalid. By getting you a green card, the employer does not have to worry about any changes in the corporate structure or in your job description. Your employer cannot use you on projects requiring certain security clearances without your green card. The U.S. government requires this for many of it's contractors.
Creative arrangements can minimize employer risk.
You can give some kind of commitment or guarantee that you will stay with the organization for a particular period of time. Negotiate a longevity bonus in your compensation plan with an incentive to stay with the company. Make sure that it is a reasonable proposal, and be sure that it overcomes their fears. Pay resident tuition. In many states, green card holders pay less tuition for College and University.