New laws are allocated in annual budgets allowing your representative or minister to tack on money (we call it pork in the USA) to their district that they tout when up for reelection. Amending an existing law precludes this pork barreling process from taking place, which would make it harder for incumbents to get reelected.
It is all about politics and money. One man's pork is another district's project employing people from that district or pay back to one's campaign contributors who contributed to you in the first place because they expect you to give back in the legislative process.
Just look at the US immigration laws to see "a dozen laws that basically say the same thing." If Obama and the US Attorney General actually enforced the current immigration laws to the letter, then we would have no illegal immigration problem. Instead, politicians sell-out, ignore illegal immigration in hopes that doing so will warm the children of illegal immigrants to their political party, try sneaky ways to get illegal immigrants to vote (hoping the Secretary of State does not review immigration status on the I-9 record) and vote against any new immigration law or strict enforcement of existing immigration law because they have a future constituency to protect and build.
