Wealth is intimately tied to access to scarcity.
This is why gold was money. But in the second half of the twentieth century, due to capital controls and the fiat standard, gold became more difficult to access. Therefore, anyone trying to preserve their wealth had to access scarcity in other ways.
The scarcity that the last few generations relied on was job scarcity. Wealthy people in these generations worked in fields that are artificially restricted in supply (lawyers, doctors primarily). To obtain these jobs, you have to be accepted to highly competitive schools and take on a lot of debt. Due to these artificial constraints, supply is reduced, and salaries are higher. These lawyers/doctors are telling their children to do the same because job scarcity is the best scarcity they know of. Because gold was largely off the table and bitcoin didn’t exist yet, a highly specialized job was just about the scarcest thing you could get your hands.
This is advice for the 20th century, not the 21st century. We have bitcoin now - the scarcest thing in human history.