Japan is so racist, they won't allow us to lurk in their stuff.
Nobody wants a niconico english account when Youtube offers a much better and bigger service for free, and allows us to browse in all the content with almost no limitation. Remember, niconico only allows you to upload up to 4Gb of video for free, and no HD quality, while youtube offers UNLIMITED and HD.
There is a lot of japanese people that is moving to youtube (and when I say moving, I mean they are uploading niconico videos on youtube), because they realise that niconico is SHIT.