Saying you can't earn more is ludicrous.
True, but these are people who don't need to earn more, they just need to not go to Disneyland.
For people around age 60 considering Disneyland, anyone could increase income, but everyone can decrease expenses.
Many people in their 50s could reduce their expenses and retire immediately, but if they increased their income, they would have to work 60 hour weeks to pull their retirement in just a couple of years. My dad started a company in his mid-50s, and he was working 80 hour weeks with little to show for it but future earnings. He could easily retire right now if he moved to a smaller, three-bedroom house.
Cutting expenses by a third is immediate and a lot easier than increasing income by 50+% and then waiting for that income to accumulate. You don't have to trade your life energy away in order to gain financial freedom.
This is why MMM is so powerful.