Take your average American newspaper, and look at the amount of news on all foreign countries put together. Then double that. That'll give you an idea of how much attention European newspapers devote to the American presidential election - just about every single day. I may be exaggerating, but not by much.
Also, I like how you suggest Britain is not part of Europe...
Uh. Yes. Keep in mind that most people abroad are either unaware or just uninterested about the things that a large group of Americans dislikes or downright hates about Hillary - whereas Trump's failings are impossible to miss, and seeing how he goes out of his way to insult other countries every chance he gets, foreigners are even less likely than Americans to forgive them.
Much like with Brexit, a vote for Trump is, in essence, a vote for 'I don't know what I want but I know it ain't this' - nobody knows what casting such a vote will actually do since there is no plan or strategy or vision behind either Trump's campaign or the Brexit's, but the people doing so are so fed up with the current establishment that they are willing to take that risk. Or they've deluded themselves into thinking that their personal interpretation of the campaign is the correct one, and all the people who view something entirely different in it are wrong. I suppose some of them will be proven right in the end, but most won't.