Have you ever asked yourself what the "Middle Ages" are supposed to be in the middle of? The answer tells us something about our biases.
See, at the time of the Renaissance and the Enlightenment (or, as my brother likes to call it, "the Endarkenment"), European intellectuals began to rediscover knowledge from the ancient Greeks and Romans that had been lost or neglected. They came to see themselves as heirs to this classical heritage, and looked upon their predecessors of the most recent centuries as poor benighted souls who had toiled away on matters that were at best insignificant and at worst frivolous superstition. So they termed the ancients as the "classical" period or "antiquity," and themselves as "modernity" or "the Enlightenment." And what was left in between? Those ho-hum "middle ages."
Basically, it's the historiographical equivalent of "flyover country."
Yeah, never mind that medieval Christian Europe invented the hospital, the university, and the fundamentals of the scientific method (thank you, Bishop Robert Grosseteste and St. Albert the Great). Never mind that they kept alive and furthered the thought of Aristotle. Never mind that they preserved the Roman legal system which still serves as the root of European law today. We'll just ignore all that. Silly moderns. What do they know anyway?