Yeah! There could be many reasons why the guy made such a big, crazy bet and lost that $1.4M.
For example, I do not rule out that this is just a contractual bet made specifically to promote and advertise such an event. Moreover, the advertisement is not so much the guy himself, whom many now consider an idiot, but the casino itself, or rather the bookmaker, through which such a big loss was issued. We do not know many details of this event in order to somehow objectively assess such an event.
And who and how much received from such a deal.
It's possible that this is all plotted from the very beginning to make a noise and stir some speculations and gather attention to the casino website the gambler has lost his millions of dollar, which to be specific, amounted to 1.4 million dollar. Since this is such a big amount, it could be happen to be sponsored. But if that's not the case, it's also possible that the gambler just happen to misclicked or misread the numbers he typed and input, thus amounting to such huge amount of money placed for a single bet.
It's also possible that he trusted so much to the point he was so sure the team he bet on wouldn't lose, but unexpected turn of event happened, thus losing the supposedly "guaranteed win". We'll never really know because there are endless possible reasons. But bottom point would be, always double check your bet, and just bet what you can only afford to lose.
There are many possibilities that could have happened in that bet and we speculate that he has written the wrong number in the bet, which means it is a very large number. And he probably didn't expect that it would cause him such a huge loss even though he might still have other money. But still he would probably be saddened by such a huge loss and he should have realized his mistake and would not repeat it in the future. But if he is a gambler who often uses big money to gamble, it will mean nothing to him because he can definitely accept whatever the outcome is. And we little gamblers should always check everything before we hit that bet button.