This is obvious to many, if not most of folks. And the answer is simple, there is no money left over each month. Add to that the fact that many employees have zero access to retirement savings accounts through work. Many employees lack a living wage, and even basic benefits, and retirement investing is not even on the radar of the next thing to achieve, it's further down the list.
Here is an article that discusses "Two big hurdles keep many Americans from saving for retirement" from Yahoo Money that was written by Kerry Hannon.