Hard to tell people they can't afford things when they have family money.
This is why family money seldom survives the third generation, in North America at least.
The first generation earns the money.
The second generation mostly screws up. It benefits from what the first generation earned, but there's a gap between the asset and the knowledge and sacrifice that produced it. They're trained to spend, but not to accrue wealth, earn an income, or manage the wealth in ways that develop an income stream. Unlike old money families, kids in second generation wealthy families aren't taught that they have to do something with their lives. They frequently end up in professions that don't earn much but their standard of living is subsidized by their parents' wealth, EOC style (Stanley & Danko). Accordingly, they pile up debt that doesn't really get discharged until they inherit. That reduces the net family worth. When there's more than one kid, the family fortune is divided. It's generally still possible to be financially independent on the inheritance, but the standard of living has to be scaled down. Unlike in old money families, there's no awareness of how you have to scale your standard of living to the income generated by your assets in order to remain financially independent and to have enough to pass to your own kids. So they gradually spend down the principal, until there's only "enough" to pay for an expensive education, a nice house, and a good launch, but not enough to FIRE the kids. (Side note: the Mustachian FIRE lifestyle and mentality is actually in line with what old money families practice when the 'stache starts to dwindle due to economic changes or too many kids.)
The third generation grows up with a near-total lack of connection between their standard of living and what it takes to achieve it. They imitate their parents' debt accumulation habits and spending habits but never accrue much for themselves. This is where you see most of the trust fund babies.
Every once in a while, you get a second generation that contains at least some people who get the cash flow concept. So they stay wealthy and sometimes even add to the family wealth, and they teach their kids to do the same. The ones that learn become the branches of the families that become "old money", while the branches of the family descended from a second-generation idiot go broke.