Interesting story but I'll give some serious pushback. #3 and your aunt's addiction were the keys to the whole situation.

No one is in total control of their income. A sustainable lifestyle is the key. If your uncle was happy and has $2-5 million in the bank, then clearly there was no need to spend time improving his investments, as his life was sustainable. The issue was with your aunt. If she has a gambling addiction and/or is unhappy with her life, it doesn't matter whether they have $20k or $2 million, it will be gone if they share a bank account and your uncle isn't paying attention.