How short is short? You can't get away from using words like "deliberately" or "obviously" in your content. So why should you try to keep all your words short?

1 Speed. Readers want ideas fast. They haven't go the time, or don't want to give it, to reading at length, unless they scan and find it interesting enough. Short words, representing ideas, are the fastest way of getting those ideas into your reader's brain. It's so so fast they can do it at a glance's pace, never mind scanning. They're the most efficient way of conveying and expressing your ideas.

2 Pointedness. One word which represents or contains an idea has complete focus on that idea. Sub-headings tend to use such words, like "speed" and "pointedness". Of course, your long word could be someone else's short word. It's an individual understanding of what a short word is. Some people can take in a word like "pointedness" very quickly, others not. However, it's better than saying "complete and concentrated focus". That would take much longer, relatively speaking, to absorb. A lot of people wouldn't bother.

3 Meaning of short. What do people mean when they say use short words? As seen, it's not necessarily that the actual words should be short in length, though that helps. Rather, it's two things. One whether you can use one word instead of a group of them. Second, that you're speaking the same language as your readers. That is, it's as near to their everyday speaking as you can get without dropping into dialect, slang or sloppy grammar, spelling, sense, and words. Also, most people use a limited number of words that they choose from to explain or talk about things. If you go too far beyond that limit they lose interest, expecting that it will be too difficult for them.