We can't really call the mentioned examples as biggest wins unless we know how much the players have lost before hitting it and how much they have spent on gambling from that money. But there is no doubt those are huge multipliers we don't see everyday.
The risk is the same (same odds for any other player). It's just those players got extremely lucky and hit the jackpot, which is something I envy them for.
Yes here some can win first time or try again and again. Some one lose more or re-spend their winning reward. It depends on them. But these wins are definitely big wins that don't usually happen. They must be among the lucky winners. We gamble more or less but how many of us get this kind of win?