Why do humans need laws in order to keep themselves safe, like bicycle and seat belt laws, instead of keeping themselves safe without actually being told to?

People are stupid, NH, ...plain as that. Our race is beset by imbeciles.  

Such 'Laws of the Obvious', as you mention, are created in an attempt to legislate Common Sense - which, in itself, presents a very sad statement. 

To quote a line from The Refreshments song Banditos, "Everybody knows that the world is full of stupid people."

Just read the warnings listed in the instructions when you buy a new blowdryer. The last one I bought had listed such things as, Do not use in the shower. Do not use while sleeping. Do not use in while in the bathtub.

Those are all there because someone actually did such stupid things. If you look at a soda vending machine, there is a warning that states shaking the machine could result in injury or death. Do you know why that is there? Some drunk thought the machine ripped him off and rocked the machine to get his soda. The machine fell on him and he died.

Basically it's just carelessness. Most people -- particularly most active people -- are optimistic about their chances of being injured. They don't think it can happen to them. So laws have to be enforced to free up space in the casualty wards.

There's nobody stupider than people

Because laws generate money, there was a time when we had the freedom to choose whether to risk stupidity, now Health and Safety has become a nightmare.

My friends and I were discussing this the other day, it has taken away our fun and a sense of freedom. It isn't for our benefit, we now live in a compensation culture, and it isn't us that get the majority of that money, the lawyers do. They want us in Court so they can play the game where they see how much more they can squeeze out of us, Game, Set and Match.  If we get hurt at work, it means days off, and or possibly indefinitely and the government want to keep us labourers/serfs working and paying tax until they cannot squeeze one more penny out of us. Then they will put us in a home charged at a rate of £5,000 a month, and take our homes that we worked all our lives for.