Life is full of uncertainty, we never know what's going to happen the next day, I watched a documentary movie where the father saves money but keeps it secret from his family, and when he dies no one in the family knows about his savings but the widowed wife eventually found out the location because the late husband told the wife on her dreams.
So it's better when you hit a jackpot you have to claim and stop dilly-dallying because the money you claimed is not yet yours better to have the money in your hands and just plan anything you want to do because when you have the money all your plan will materialize.
You're right though if I'm in a position to win big from lotto I'm so going to claim my cash the next day or same day if possible cause life is too short and anything is possible, you never can tell what could happen the next day and even though I don't disclose it to all my family members maybe due to lack of trust, I'll atleast inform one or two person to be aware incase anything happens.
But on a second thought times are bad and the heart of man is becoming greedy and evil lately, in every family there's always a black sheep and you never can tell who would be plotting on steal the money so I feel maybe that's why some individuals just keep it to themselves and decide to claim afterwards, but then they could just claim it keep the cash even though they don't intend telling any family members.