What is the objective of writing? To communicate. You may be convincing others of your positions, or you may be storing some information so that you can communicate it, through time, to others who may need it later, but always your objective is to communicate.

If your objective is to communicate, then you must place a premium on being clear and specific. What is more clear than a a short, simple word? If you use a short, simple word, then you're less likely to use a word that your reader doesn't understand, which means that your chance of communicating is maximized.

What about communicating what you mean? Well, to communicate exactly what you mean, you need to choose the exact word. Your chances of choosing the exact word are maximized if you're choosing from a large set of words, and you most likely know a lot more short, simple words than you are long, complex words. So maximize your chances and choose the short, simple word.

Short, simple words are also safe. You can be quite confident that you know what you're saying, unlike when you're using big or technical words.

So stick to short and simple words. They're easy and safe for you and for your audience.