I hope you're not assuming that retirement means "sitting around doing nothing". Early retirees are the travellers; the people who volunteer (much needed now that most wives work); the people who can afford to take lower paying jobs such as social work; the people who are starting their own consultant businesses (and providing jobs for others); etc.
Early retirement is really a bridge between different stages of life. It's not the retirement our grandparents had (if they lived long enough to retire, that is)
Early retirement is great as long as it's paid for by the individual --- I mean retirement that means you're going to sit around doing nothing but depend on the government.
Just from people in my family --- a woman retired at age 62 and does sit around doing nothing much -- no money for her pills much less travel and she does nothing but complain about how little she gets from the government. My father still works and is in his 70s and travels very well as did my grandfather who worked into his mid 80s. There is usually more money for better trips when there is still an income. Social security isn't enough to live well from and far too many people expect the government to provide it all.