Following from your rephrasing the question in another comment-
There are a number of different factors which each partially explain the English cultural amalgamation, and of course as you acknowledge and to reiterate the points of earlier posters, France and Italy, as with the rest of Europe, are not homogeneous themselves.
But as to why England has the particular mix that it does, I would first expand the question to include Britain as a whole, and actually point to the relatively more isolated nature of the island as one explanation. Though maritime trade has had a significant impact on the island and tying it to continental cultures (this is how the Celtic, Scandinavian, and Germanic influences got there), Britain was still somewhat out of reach of many continental conflicts and kingdoms, so that their influence has been less consistent for much of history. While most of England was part of Roman Empire for a few centuries, it was on the edge of the empire and far from the cultural hub of Rome. This may be the strongest factor in your point about Romantic language influence. In addition, the fact that Rome never completely conquered the island of Britain meant that Celtic and prior cultural remnants had even stronger roots to persist in modern-day Scotland and Wales, which inevitably interacted with England.
Similarly, after the decline of Roman influence, when Germanic (I'm including Scandinavian in this category) peoples traded with, then immigrated to England, though they persisted longer and had a more significant impact on modern language in particular, they did not entirely overwhelm what existed before. Take London, for example, which has been around in some shape or form since about 47 CE. And again, on the periphery of the island, in the highlands and western hills and forests, previous inhabitants and cultures still held sway. Really the theme here is that Britain's relative inaccessibility meant that migratory and trade patterns couldn't totally overwhelm the island at any given point. Because of this, and the lack of a strong particular cultural structure or unified ruling hierarchy to be maintained or easily hearkened back to, it was also difficult for new conquerors to assume full control.
Come William the Conqueror and the Normans, and though his name does rightly suggest more success in this effort, the theme persists. Thanks to previous unification efforts under Aethelstan which were maintained through the time of Edward the Confessor, William at least had a throne to assume, and some measure of control over most of the southern half of Britain. Under successive Norman rulers, this attempt at a hegemony was able to push further into Wales, but it wasn't entirely successful and was largely halted moving into Scotland. It was during this Norman period that most Latin or Romance influence on the English language actually comes about- it wasn't some remnant from Roman times, but a secondary impact. That's why you'll notice loanwords in English generally come from French and not Latin. However, French was still the language of the elites and not necessarily the people, and Norman rule was less a migratory period and more a cultural integration of the ruling class. Because the elites are generally the literate group, and writing things down and putting them in official documents can have a much greater lasting impact on language, the Normans were able to influence English much more significantly in a relative short period of time, especially given their recency before the development of 'English' and greater push towards some sort of codification of languages with writers like Dante or Chaucer.
Finally, with the 100 year's war, England was split again from Normandy and the continent, and had never been truly under 'French' rule as we know it, so now as a more unified nation was able to continue developing and solidifying its own cultural identity with the amalgamation of pieces it now possessed.
Hopefully that answers your question at least in a roundabout way, and for further reading, I would recommend actually diving into some of the earlier sources (or annotated versions) of Bede and Orderic Vitalis.
Additional sources:
Bates, David. "Normandy and England After 1066." The English Historical Review 104.413 (1989): 851-80. JSTOR.
Lovis, Claire. "Celtic Influence on the English Language." The Influence of Celtic on English. University of Toronto, 2001. http://homes.chass.utoronto.ca/~cpercy/courses/6361Lovis.htm
Otter, Monika. "1066: The Moment of Transition in Two Narratives of the Norman Conquest." Speculum 74.3 (1999): 565-86. JSTOR.