I was one of those that looked at retiring at 55 four years ago but couldn't because of two reasons. 1) My main retirement fund, my 401k, had suffered badly in 2007 and 2) I needed health care coverage supplied by work. Those two issues are no longer issues because the 401k rebounded nicely and I can now get reasonable health care coverage through the state plans set up by the ACA bill (Obamacare). It also helps my house is paid off as well. Regardless of my situation, I've known a number of others that held off because their savings plans lost value and the need for health care coverage. One of the main benefits I see with the Affordable Care Act is the ability to un-tether yourself from your employer because pre-existing conditions made it impossible to get reasonable cost health care without them.
The decline in union involvement, if that is what is meant by "labour participation" reflects a maturing of the employer/employee relationship. No longer do we need community destroying strikes to obtain a living wage and decent working conditions.
The pendulum swung to far in one direction, it has swung back now. The auto sector is more rational, jobs aren't being lost because of over-generous retirement and benefit packages.