My brother and I built our own stash (he relies on an advisor), but I do think there is something to preparing heirs to receive wealth. Otherwise, it’s winning the lottery, and we know how that ends up rapidly disintegrating a fortune under poor money management skills, demands for support from shirt tail relatives, dumb investments, dumb marriages that end in divorce settlements, feeding addictions, etc. It’s no different with an estate.
Money is like a gas - it wants to escape - so it needs to be contained at all times, and that takes training, skill and discipline.
I also understand wealthy people not wanting their relationships with heirs to be “infected” with the possibility of receiving money from them at one’s death, which is a second unpleasant topic, so they decide to ignore the giant green elephant walking around in the room, and let whatever happens happen. In fact, as discussed here, there might well be nothing happening. No one can predict.
Just my observations. YMMV.