Homo sapiens are competitive animals. Competition is the driver of innovation, ideas, progress and growth,
Winning the competition brings money, respect, titles, promotion, recognition, personal satisfaction. Not all are solely motivated by money.
That some individuals achieve greater wealth, influence and power is inevitable. Most eventually realise that they will never be a contender and pursue other of lifes goals - family, hobby, work-life balance etc.
Many build small workshops, buy woodworking tools and machines, produce furniture, boxes, chess sets etc. They won't rival Chippendale or Rennie-mackintosh but find satisfaction in their hobby.
When the state pension was introduced in 1909 (~decade before DoE was born) very few lived long enough to claim it. We now typically live for ~20 years post normal retirement age.
It would be (IMHO) unfair to expect those working to fund the pensions of those retired who are still fit and able. This means that those who wish to retire early need to make their own provision.
Fortunately employment opportunities are increasingly flexible and varied - many choosing to work part time as they advance in years.
To keep on topic this is effectively what the DoE was doing. That he lived in some luxury was testament to his ability to win (over others) the affections of a future monarch.
Do I envy him his wealth - no. I am reconciled to my relatively comfortable existence in retirement and would not have wished the continual public spotlight he endured.
Should the wealthier be taxed to provide extra for the less fortunate is a fair question. That which increases aggregate wealth for society as a whole is good. Pursuit of "fairness" is admirable but we need to explicitly understand the cost. Negative emotions - envy, anger, etc - are very poor reasons.