On the surface, it seems like a no-brainer: wait until you're 70 to claim Social Security and your monthly checks could be as much as 70% higher. And yet a scant 3% of men and 5% of women actually wait that long to claim benefits.

What gives?

While the reasons are ultimately personal, there are three major factors that likely contribute to such a small cohort waiting until 70 to start receiving Social Security. Two of them are somewhat depressing, while the third is much more uplifting.

Elderly couple walking on beach.

Image source: Getty Images

1. Out of work and need the money

The economy is changing -- and so are lots of jobs. As automation mimics skills that were once reserved for low- to middle-income workers, and other jobs are shipped overseas, many Americans in their late 50s and early 60s are finding it difficult to hold down gainful employment. They simply don't have the skillset that many employers are looking for.

A recent survey released by the Nationwide Retirement Institute (NRI) found that 28% of recent retirees specifically cited "laid off or unemployed" as the main reason they decided to claim benefits before full retirement age. Additionally, 51% of recent retirees said they needed the money "to pay ... living expenses," and 30% said they had "no other source of income."

Clearly, many are in a bind financially, and Social Security offers a lifeline to help ease that burden.

2. Health isn't holding up

Sadly, many Americans are also finding that their health is giving out before they'd like to retire from the workforce. In the very same survey, 24% of those who claimed benefits early said they did so because they "have a health issue."

Older businessman staring at a phone in an empty office building

Image source: Getty Images

And this isn't limited to life-threatening conditions. Other research by the Government Accountability Office (GAO) has shown that 70% of those working in farming, mechanics, construction, or as machinery operators will retire before they reach full retirement age. As blue-collar workers age, their bodies' ability to withstand the chronic physical stress of their jobs simply breaks down.

3. Happiness is calling

There is, however, reason to believe that not waiting until 70 is a great thing for individuals and society as a whole: retirees are the happiest cohort of people in the country. Consider these findings from a survey by Merrill Lynch and Age Wave. Participants of different age groups were asked how often they feel certain things. The results speak for themselves:

Chart showing differences in how people feel over time

Data source: Merrill Lynch/Age Wave

The fact of the matter is that while some worry about financial concerns in retirement, they often underestimate their powerful ability to adapt to new material circumstances. At the same time, they underestimate the equally powerful benefits that freedom of time offers up.

All in all, there are lots of reasons people don't wait until 70. The important task for soon-to-be retirees is to prioritize what they want to get out of retirement, how realistic it is to assume they'll work for as long as they hope to, and how the timing of Social Security could affect both of these things.