AFAIK this election was triggered by Farage because he’s being investigated for some issues with donations and the outcome would be a sanction and trigger the same election, this way he can present himself like the people chose him and it wouldn’t have the sanction against him in the public opinion.

The thing is that if he is elected now, it doesn’t mean that the investigation is stopped, it would continue and find as he did things wrong and trigger the election.

Not presenting candidates against him from the major parties don’t give legitimacy to his shenanigans and don’t waste time and resources on a process that will be done again a few months down the road.

1. he will be winning the post uncontested, exposing the theatre play he setting up. Though i'm not sure if his supporter understand that.

2. resigning mean only quit the current post he's holding, basically vacating the seat and trigger a by-election, because a seat cannot be left vacated if the next election is still far away. he's still eligible as a candidate. It's very different than quitting a job

These is a tradition that parties don't stand a candidate in other parties leaders' electorates.

It's 100% bullshit.