Your parents are multi-billionaires. They love you, but they insisted you live a normal life so you don't have access to any of their wealth or connections. They raised you, fed you, kept a roof over your head until you were 18 but that's all.
Would you be upset if you were not included in their will, instead they are choosing to donate their fortune to charity?
Would be more annoyed in that scenario that they cut me out of their connections (which can be worth more than the money itself) and wealth while alive. If the hypothetical folks were dicks all along and I knew they had no intention of leaving me anything, I'm not sure how much that would specifically bother me compared to the overall treatment. Frankly, on principle (and because that upbringing would result in a different personality) I'd probably try to amass a fortune so I could use to undermine everything they built.