Said aloud, longer words flow more quickly than short ones, just as “convertible” has more rhythm than the double pop sound of “rag top.”
The hard stock of English words comes from our Anglo-Saxon heritage. In addition to function words such as prepositions and conjunctions, the Old English word hoard contained many stark words of one syllable, including the notorious four-letter variety. That hard language was softened in 1066 after the invasion of England by William the Conqueror. The Norman (think French) king brought with him a language that sounded more sophisticated.