My biggest reason for considering early retirement is that I can just about afford to do so. This isn't because I'm hugely rich, but because my outgoings are low. Most of the things I'll do in retirement are low-cost activities: walking, reading, gardening, cycling, playing guitar and learning the lap steel and Appalachian dulcimer.
Also, I might not have much time left. None of my grandparents got past 80, and my dad didn't see 70. This gives me a double reason for retiring early. I want to live before I die. And it means I can run down my wealth because I might not need to provide for a long life or for social care. Also, I have no dependants to whom to leave a bequest.