Probably because their supporters couldn't cope with anything more intellectually taxing than putting a cross against a name - and the reason their vote is so low that they probable put it against the name they don't want at that!

I was going to say that that is being rude to those who are only able to do this, Andrew.  However, if you look at the membership lists, they include well-educated and responsible adults - so the argument you put forward doesn't stand up to scrutiny