Because the record is important. A written contract is preferable not because it's any more or less clear than a verbal one but because it is written. There is a tangible object recording all the pertinent details and marked by both parties to indicate that they agree with it. Those parties can still contest the contract based on what they think the words mean, but neither of them can lie about what the contract actually dictates.
Originally Posted by Selfsim
The simplest example of why it matters where a person comes from in what they say is that different words mean different things in different places. There is a word that, in the United States, is an innocuous, even childish, term for the human buttocks. In the United Kingdom, it is a rather rude term for the female genitalia. Not a lot of people from either country, so far as I can tell, know what the people from the other country use that word to mean. There have been fights about that on this very board.
And you know what? To a greater or lesser degree, it does matter what your scientific background is when you make pronouncements about science. You aren't guaranteed to be right, of course, but you are more likely to have the basics down and not be quite as wrong if you are speaking in a field you actually studied seriously.
"Now everyone was giving her that kind of look UFOlogists get when they suddenly say, 'Hey, if you shade your eyes you can see it is just a flock of geese after all.'"
"You can't erase icing."
"I can't believe it doesn't work! I found it on the internet, man!"