If those of you who talk about this are Indonesians. So I think you will know that actually Indonesia has long banned adultery or having sex outside of marriage. even in the source you linked it was also explained that the law regarding sex outside of marriage had existed before but was not enforced. and the new law has only been slightly modified or clarified, namely to prohibit sex outside of marriage in its entirety.
while the old law only prohibited sex outside of marriage with non-married couples themselves. like the prohibition of the husband having sex with women other than his wife.
The reason why people ignored the law is because it was stupid. It has been long debated whether we should obey laws that are outright stupid or oppressive.
Let's say that someone decides you no longer can use a mobile phone, or that you are not allowed to drink alcohol, even at home. I feel like there's a huge difference between not allowing married people to have sex outside marriage and not allowing any unmarried couple to do it. Having sex is a natural human interaction. People meet, start dating, have sex, get married - this is how it's done everywhere.