B/C it didn't actually happen that way. The "Dark Ages" is a myth perpetuated in elementary school to children. The "Dark Ages" referred to the 100-200 year period immediately after the fall of Rome, during which Western Europe was thrown in relative chaos. After that however, Europe was fairly vibrant, and new inventions were churned out over the next several centuries (mostly military, agricultural, and metal working technologies).
Italy never lost its luster as a center for science and research; even after Rome's fall, the climate, location, and trade made it attractive to inventors, architects, and artists--the Vatican did not fall.
For example, the earliest patent systems, (yes, plural) predated the reintroduction of Classical texts into Europe. Many European scientists and mathematicians independently came up with ideas similar to the Ancient Greek dudes, but don't get popular credit for this because they weren't first.