Quite simply, because he's an antisemitic, racist idiot who when in here would go whipping up hatred and thus is not wanted here. We kicked out Geert Wilders, and we kicked out Salah again. PSC whinging doesn't count, and the security of the UK should come first.
Nigeria says troops destroy extremist camp, rescue 178 people (AP)
from the article: Islamic Movement leader in Israel arrested in London