Can anyone tell me why Labour just threw another election?
Because they know they will lose. Labour's Brexit policy is not clear at all. Watch Emily Thornberry of Question Time 5 September 2019. Her policy as foreign secretary, if in power, would be;
Negotiate a deal that protects Jobs, etc., then campaign to remain!
The entire audience roared and it was made up of 52% leave and 48% remain.
Labour's conundrum is that the leave votes were mostly from labour heartlands. Figures have been challenged (by remain supporters mostly), but estimates are;
60% of labour voters also voted leave.
148 labour constituencies voted leave
84 voted remain.
Polls also show that people fear Corbyn as PM than they fear no deal. So that is another nail in Labour.
So Swinson of LibDems has said that even if there was a further referendum and vote was to leave, LibDems would not accept the vote. Audience roared at that too on Question Time. If it is LibDems policy to ignore voted why do they call themselves Democrats?
Johnson called an election because he knows he will win. Even if Conservatives did not get an overall majority, they could team up with Brexit Party and make a coalition that would have a majority.
Remember in 2016 there were 406 constituencies that voted leave and 242 that voted remain. A coalition with a majority of that magnitude could easily overturn the Benn Act so release UK from the EU shackles.
Johnson would then make the same statement as before;
Backstop = No Deal
No Backstop = Deal
However, on BBC news it is reported that Finns and French will say it is over if Johnson has not produced Backstop alternatives by end of September. Music to Johnson's ears.