Nineteenth-century Romantics are a major source of our current understanding of the Matter of Britain. Their involvement has codified the versions of the stories now most often thought of as "canon" by enthusiasts of the legends, smoothed out the conflicts between different stories, and thus leveled off a lot of the detail of interest to the historical folklorist that's found in the early sources. But their interest is also why the Matter of Britain is well-known at all - today, few people other than enthusiasts of medieval history or French literature can tell the story of the death of Roland, few who haven't studied the classics could give you a summary of the life story of Alexander the Great or any part of the history of pre-Homeric Thebes, westerners know the Romance of the Three Kingdoms and the Journey to the West only if they study East Asian culture in at least a little bit of depth, but King Arthur has been on Broadway twice, riffs on the story can draw big box-office crowds in part by trading on how they differ from the classic story, and as much as it departs from the traditional plot, the BBC's Merlin can still expect the audience to feel like a significant moment just happened when an episode ends by revealing a child character's name to be Mordred.
Arthuriana, in other words, is undergoing a revival. The revival began nearly two hundred years ago, and has not ceased. Its greatest expression is perhaps TH White's The Once and Future King, which manages to play games with the nature of its setting, explore deep themes of war and peace not addressed in the original material on which he draws, and captivate new audiences each generation, all while remaining mostly faithful to his main source, Malory's Le Morte d'Arthur. To others, the best known form is Marion Zimmer Bradley's The Mists of Avalon, while others are most familiar with Monty Python and the Holy Grail.
To many people, the canonical version of the Arthurian stories is the version recounted in Tennyson's Idylls of the King, a series of ten narrative poems. Most of the poems tell stories from Malory, and like White Tennyson chooses to present the tales in a way that is faithful to the source but that explores the tensions of the early Victorian period and the coming of industrialization. His work is peppered with descriptions of nature. While many modern people who haven't delved into Arthurian material are unfamiliar with Tennyson's tellings, most expect the life and death of Arthur to proceed according to his version. It is this version's quest for the Holy Grail and list of canonical knights from which Monty Python seems to playfully deviate, not because they wished to riff off Tennyson but because they wished to start from the story as understood by their audience; while the Pythons made the unexpected choice to leave out Morgan le Fay, Mordred, and Guinevere, even audiences who are most aware of their version recognize these characters and know their stories in a way that conforms with Tennyson. On the other hand, characters that are highly significant in other historical versions, such as Blaise, are less well-known; Blaise's absence from Tennyson and insignificance in Malory probably have a lot to do with why.
Our entire ongoing Arthurian revival, therefore, is still constrained by the mold set for it by the Romantics. Without that mold, the Matter of Britain is a fascinatingly polyphonic set of stories that don't quite fit together but are each well-suited to the needs of their time - but without the same forces that collapsed it into a coherent whole, it would probably be obscure to us today.