Among recent retirees, the top consideration in leading them to leave the workplace was not their employer's retirement program.

Instead, according to a Towers Watson survey, workplace disengagement and workers' eligibility for Social Security and Medicare topped the list.

In addition, 20% of those recent retirees said one of the key factors in their decision was disengagement with their jobs.

One reason the report said it's important for employers to understand what drives people to retire is that, in the coming flood of boomer retirees, employers will have to be able to manage the departure of employees who are in critical positions.

Other factors include the changing role of employers and the waning traditional model of full retirement age at a fixed date.

While data are available on some of the factors that cause people to retire — such as age, health, family circumstances and employer incentives, all of which can vary in importance with the age of the worker — there isn't so much information available on the thought processes and motivations leading up to retirement.

While more than a quarter of respondents listed employer incentives, such as retirement eligibility and retiree health benefits, as their main motivation, more recent retirees were focused on other things.

And as employers cut the benefits available to retirees, they have less sway over workers' decisions to retire.

In addition, there's the question of how retirees felt after retirement.

Those who felt pushed out by the pressures of work were more likely to say that they were worried about their finances; they were also more likely to be shocked by retirement and be sorry they left the job.

Among those who cited reasons related to their working environment, the overwhelming majority said that feeling disengaged from their employer, their job or both played a pivotal role in their retirement decision.

On the other hand, those who retired to take advantage of employer incentives, or because they were eligible for employer benefits, were less likely to regret their decision.