A pre commitment will just mean that people addicted to gambling will nominate a sum far higher than than they possibly intend to lose - a just in case attitude. which means that they will possibly bet more than they would have without pre commitment. It's called the law of unintended consequences.
When will governments realise that it is difficult to legislate against human behaviour, especially when it concerns those with an addictive personality. This goes for drugs, cigarettes or alcohol. Provide help for these people instead of laws or taxes, but there's no revenue in help!
