By the same token, if you were to write a contract in non-legalese, it would be more open to interpretation simply because the language hasn't been as thoroughly tested in the courts. Sure, if you're clever and write clearly then that might not be much of a problem, but are you really smart enough to write a contract that doesn't contain any unintentional loopholes that the other party's lawyers will pounce on if given the chance? A misplaced comma can spell disaster. That's one thing lawyers tend to be trained to do: using language that courts understand and agree on the meaning of.

To compare it to programming, I think of legalese as crufty code that simply remains in use because it has always remained in use, and ugly as it may be, we all know what it does. Woe is the young upstart developer who tries to rip it all out and replace it with something modern, much to the consternation of the greybeards who had a mutual understanding of how things have always worked previously.