Why? It’s not compulsory, lots of people bet responsibly and enjoy it.
Not for any moral reasons but just because:
a) Other people’s bets are as interesting as other people’s dreams and other people’s kids
and b) It leads to really awful, abusive online behaviour. Just look at Rene’s words about the ref. Often the racial abuse of players you read about after missed penalties, own goals etc. is from people complaining about the bets being ‘ruined’.
Oh and c) it ruins lives. Maybe that is a moral reason.