There are people who actually think it's an investment because they are being deceived by others. It's just like someone I know that told me that he had a means of getting sure odds of 1.15 daily and he told me that it's hundred percent sure, he considered this an investment and he went all in. He staked huge amounts of money getting back just little profits this made him very sure of it and overconfident until he ended up losing a huge amount of money. Gambling will always be an expense no matter how sure it might seem
I've heard many cases of people who were not able to get it right in games with high odds and for that reason they started betting on games with very low odds, something like @1.10 odds, but these people gave up after a long time because they realized that it was not profitable to place bets with low odds.
I believe that even if your friend had not gone All In, over time he would have realized on his own that placing bets with very low odds is not profitable in the long run. Even if he also placed bets with high odds he would also lose in the long run. Everyone realizes this at the end of the day.