Growth in capital has been exceeding growth in wages for decades now, and by increasing margins. Ergo, the best way to get rich is to start rich. Take a look at the wealth-distribution curve worldwide and you can see that this is having exactly the impact one would expect.

There are more millionaires in developed countries these days because "millionaire" by now basically just means someone who can afford one (1) biggish house before they die. The reality for most is living from month to month and never having the slack to risk taking time away from work. That's structural, and no amount of positive thinking is going to change it.