“Why on Earth are we actually having this election?”
We are having this election because Theresa May (and the Grandees at Central Office) were convinced by the anti Labour (anti Corbyn) popaganda from their allies in the media, that she had a 30% to 50% lead in "the polls" and that she would have a landslide victory at a general election with an overall majority of at least 200 seats. The allure of a massive overall majority was too much for her conceit to resist and in an unashamed act of cynical opportunism she called a gereral election and had the effrontery to say it was only to secure a mandate from the British people to conduct Brexit negotiation.
It has nothing to do with Brexit. It has everything to do with vanity and cynicism and the beleif by Theresa May and her government, that they cn deceive the British people with lies and duplicity and moreover that the people will beleive it.