Has there been an official reason why Dracula wanted to go to England, and hadn't gone sooner in the 300 years he’d been alive? In any form of writing? His reason he explained to Harker in the original novel was obviously a lie.
The Count's reasons for coming to England are never explicitly s-p-e-l-l-e-d out, but at the time Dracula was written England was THE world power and London was pretty much the capitol of the world (at least as far as a British author was concerned); anyone with aspirations would OF COURSE move to London. But there are hints that the Count wanted to expand his power, possibly even creating a new monarchy of vampires. It took him so long because Stoker's vampires are little more than animals when first created. It took the Count a long time and great strength of will to re-learn how to be "human".
Here's a few quotes from the book to support this:
ch. 4 Jonathan Harker's Journal (cont.):
I shuddered as I bent over to touch him, and every sense in me revolted at the contact, but I had to search, or I was lost. The coming night might see my own body a banquet in a similar war to those horrid three. I felt all over the body, but no sign could I find of the key. Then I stopped and looked at the Count. There was a mocking smile on the bloated face which seemed to drive me mad. This was the being I was helping to transfer to London, where, perhaps, for centuries to come he might, amongst its teeming millions, satiate his lust for blood, and create a new and ever-widening circle of semi-demons to batten on the helpless.
ch.23 Dr. Seward's Diary:
[van Helsing] “I have studied, over and over again since they came into my hands, all the papers relating to this monster, and the more I have studied, the greater seems the necessity to utterly stamp him out. All through there are signs of his advance. Not only of his power, but of his knowledge of it. As I learned from the researches of my friend Arminius of Buda-Pesth, he was in life a most wonderful man. Soldier, statesman, and alchemist—which latter was the highest development of the science knowledge of his time. He had a mighty brain, a learning beyond compare, and a heart that knew no fear and no remorse. He dared even to attend the Scholomance, and there was no branch of knowledge of his time that he did not essay.
“Well, in him the brain powers survived the physical death. Though it would seem that memory was not all complete. In some faculties of mind he has been, and is, only a child. But he is growing, and some things that were childish at the first are now of man’s stature. He is experimenting, and doing it well. And if it had not been that we have crossed his path he would be yet, he may be yet if we fail, the father or furtherer of a new order of beings, whose road must lead through Death, not Life.”
“He has all along, since his coming, been trying his power, slowly but surely. That big child-brain of his is working. Well for us, it is as yet a child-brain. For had he dared, at the first, to attempt certain things he would long ago have been beyond our power. However, he means to succeed, and a man who has centuries before him can afford to wait and to go slow. Festina lente may well be his motto.”
ch. 24 Dr. Seward's Diary:
[van Helsing] “The Count is a criminal and of criminal type. Nordau and Lombroso would so classify him, and qua criminal he is of an imperfectly formed mind. Thus, in a difficulty he has to seek resource in habit. His past is a clue, and the one page of it that we know, and that from his own lips, tells that once before, when in what Mr. Morris would call a ‘tight place,’ he went back to his own country from the land he had tried to invade, and thence, without losing purpose, prepared himself for a new effort. He came again better equipped for his work, and won. So he came to London to invade a new land. He was beaten, and when all hope of success was lost, and his existence in danger, he fled back over the sea to his home. Just as formerly he had fled back over the Danube from Turkey Land.”