> yet Wikipedia continues to use the term “Dark Ages” as the article title.
The article is about the history of the term "Dark Ages", why shouldn't that be the the title? If you go by link counts, there are 741 links to the Dark Ages page but 2582 to the Early Middle Ages instead.
> Why don’t they use the term and what term is preferred instead?
"Dark Ages" is itself somewhat ambiguous. In its original incarnation, it referred to the entirety of the time between the "Fall of Rome" (itself hard to specify) and the Renaissance, as its early users saw Rome as the pinnacle of human civilization and looked down on everything following the end of Rome as unimportant, at least until they themselves were bringing back the splendor of Roman civilization. Later scholars were instead nostalgic for the High or Late Medieval civilization, so instead they narrowed the term to exclude their favored era, resulting in it referring to only the Early Middle Ages (to ~1000). Some people go further still and exclude the Carolingian Renaissance from the Dark Ages, pushing its end date further still to 800--there's no neat alternative term for this range, but Age of Migrations covers much of the themes.
In any case, periodization of that time period of European history is immensely challenging. The decline of the Roman Empire brings with it a decline in the written record and our knowledge of events in the period diminishes drastically, only recovering with the Carolingian Renaissance. Furthermore, the Roman Empire doesn't fall in an easy cataclysmic moment (there's no Battle of Hastings here), but instead disintegrates at different rates in different parts of Europe, with the final vestige only falling in 1475 (Principality of Theorodo). Meanwhile, there are several overlapping themes going on: the rise of Post-Roman kingdoms (such as the Franks and the Lombards), a mass migration of peoples (including the Anglo-Saxons and various Slavic groups), the Viking Age, the birth of Islam, the Great Schism between Eastern and Western Christianity (and other schisms within those sects!). For the boundary between the Middle Ages and the Early Modern, you can point to "about 1500" and note that several major changes happen about the same time (including total conversion to gunpowder weapons, Protestant Reformation, discovery of the New World, and the Fall of Constantinople)--that doesn't exist between Antiquity and the Middle Ages.