They're unwise to go public, they're open now to constant harassment which will continue forever. All sorts of fake and legitimate sob stories, and the rest. It would be worth a mob kidnapping some relative. If it was 5 or 10 mill to get them back they'd pay it and we'd never hear. There are clever teams of people out there.
Years back I did some work for a close rel of a well known rich guy over a longish period. All the extended families' kids had drivers and minders for good reason, as various of them had had trouble. I was checked out when something somewhere happened. His wife apologised - all a bit spooky.
These winners will have intermediaries for appeals, communications etc but if some attractive bright kid's family asks for £5m for an operation to save their life and the couple say no, the gutter press would probably publish it.
The lottery people do have advisers, to put the cash somewhere discreet.
If they let people know thay'd won say £3m, they could explain cars, house etc.
Being predudiced (or experienced?) about some of the things I noticed in the interview, I thought immediately that it would go badly if left to them.