Because they trust their team in sports betting, while in gambling (dice/blackjack/etc) are purely luck based + added house edge.
Not only trusting, because if it's trust only, you'll never have a success in sports betting.
Every match has different odds, no matter how you like your team to win, they could also loss at a slim chance, but if they will win, you'll
never get a good payout since for sure the odds is low. Trusting a team means they are good and when they are good, their betting odds are low.
Before anyone can trust a team, they would probably have known a lot about the team which included the odd and the chances of either winning or losing. The reality is that many who bet high do that because they feel they can trust their club and that is what the above poster is trying to say.
There might actually be other things to put into consideration and this is what we call skills especially with been good at analyzing a game, but it takes more of trust to make a high commitment on a bet. Trusting a team does not mean they cannot loose, it only means they have better chances of winning and this is the reason one can commit high money.