I think it's easy to fall into a tailspin of reasons and factors trying to answer this.
Stuff like the media helps (well, hinders) of course, but I think the root and deeply unfortunate reality is that large swathes of the electorate are just irredeemably dismal cunts. A lot of the more insidious current policy and posturing that gets rightly derided on communities such as here and Twitter simply plays well with an unfortunate amount of British voters.
It's why I think we have to be careful about calling this lot incompetent or idiots. The play for the absolute worst traits of British culture and outlook is an intentional power grab and I think it's been extremely effective. Cynical, but effective.