Before the rise of the ideal of the "self made man", the nobility was popular, not because they were rich or nobles, but because their self-sustaining income meant they could engage in things society needed but were not profitable at the time, like science, art, culture, defensive military (of course, being a mercenary, or a plunderer, is quite profitable), and so on.

When the industrial revolution happened, the necessity for workers, in all levels, including managers, directors, and so on, made necessary for society to invent a reason for people to do those jobs, to change their old ways, then it became honorable to be a self made man, a guy that would use hard work to earn his income, instead of being a noble.

It was that time, that then being a noble became a thing to be derided for, and of course, the behaviour of many nobles did not helped things for them.

But originally what made a noble, "noble", was being to sacrifice himself, and do what needed to be done, without expecting payment, and he could do that because he already had income (usually in the form of some contract with people that farmed his land, be taxing them, or loaning the land to them, or something else).