We are saying is that a) there are strong reasons a player who's earned $48M might want more and b) it's likely that in many cases his grandchildren and great-grandchildren won't be rich people, even if the player is moderately responsible.
...right, which is pretty much the definition of what "generational wealth" actually means, since it's got to cross, ya know, generations. johnmd's logic seems to be "that's a fuckton of money, therefore it is 'generational wealth'."
Could you or I make it work? Sure. Suppose you end up with $25M after taxes, sitting in a brokerage account. You target a 5-6% nominal investment return with ~2% going to inflation, maybe .5% to money management, and plan to take out ~3% a year for living expenses. That'd be ~$750k gross, less LTCG (20%) so $600k net => $50k / month to spend. If you're a just-now-former baller living in some 8-figure mansion, that $50k goes up in smoke real quick. Got 10 cars, because you thought your NBA career was going to last forever? Gone. Jewelry, travel, partying, etc. $50k / month is really not that much by pro-athlete standards, even if you're generally a low-maintenance kind of guy.
Now instead let's say you try to cut that back to $30k/month, so that you can actually build some principal appreciation in. THEN maybe you grow the pot big enough that your kids can start their adult lives off with private school, a free college education, and some help getting a place and covering some ordinary expenses as they settle into a career. But
how many kids? Let's say you
don't grow the principal faster than inflation, and so you end up with $50k/month in 2019 dollars going to, say, 5 kids. An extra $10k/month would have fucking rocked when I was 22 years old, but it's not quite what I associate with "trust fund money". And then you need to consider that your kids will likely reach adulthood while Daddy Baller is still around and kicking and quite accustomed to his lifestyle - enjoying his spending, even if he's not overspending. So maybe for a while he cuts back a bit and the kids have to take less. Or, god forbid, he dips into principal (which makes it by-definition not generational wealth).
All of those numbers assume you're not getting advice that helps you put it into an irrevocable grantor trust and avoid a good chunk of taxes. And of course, trust executors need to get paid too, etc. But generally we're not talking about a pot of money that is going to make things even cushy for the kids, nevermind the grandkids.