That is because getting $1M plus was enough for me to hire a servant who can wash my car, clean my swimming pool, work on my garden, and serve me meals and cocktails when I ask him to. Hiring two servants would not make me happier.
It still seems to me that pool services, car detailing services, gardening services, housekeeping services and Door Dash would be a less hassle and more cost effective way to outsource those tasks. But if you value the status of having a full-time "servant" then it was worth it to you work ten more years.
I like to read up on happiness studies like you have mentioned, and newer studies have concluded more money may be better than the oft quoted $75K annual income study. However, these newer studies usually mention factors like financial security, having good health care, control over one's life and not having to worry about losing your job. Most posters here, even those retiring 10+ years early, planned enough to cover those factors. I've never seen a study with factors like having a private beach or personal servant in any happiness study, but if you have a link I would enjoy reading about it.
Related link on a new Wharton Study:
https://www.cnbc.com/2021/01/22/new-wharton-study-people-are-happier-when-they-earn-more-money.html -"During the Covid pandemic, income could matter a bit more for people’s happiness, Killingsworth says...“For example, if you have a financial cushion, you’ll be more able to ride out a period of unemployment, and if you have a high-paying job, perhaps it’s more likely you’ll be able to work from home and keep your job in the first place, all of which would give you more agency over your life,” he says...Ultimately, Killingsworth says that income is just one factor that influences an individual’s happiness — not the most important one. “If anything, people probably overemphasize money when they think about how well their life is going,” he said in the release....
Indeed there are many factors besides money that contribute to a person’s happiness: Other research has shown that social relationships and connection are the most important contributors to happiness...Another thing to consider is how our work and earnings fit into our view of success. In Wharton study people were asked, “To what extent do you think money is indicative of success in life?”
Those who equated money and success were less happy than those who didn’t hold the same view."