Why not bet on a West Brom win outright?

Because their last two duels ended in draws, 1-1 then 0-0 , and because Burnley, even in rebuild mode, remain tough to break down. The double chance covers this draw scenario.

Burnley are coming from the Premier League, aren't they stronger?

The higher level hasn't been reflected in their results: no wins and no clean sheets in their last six outings. And the transfer window could still drain their squad before the season starts.

What if Burnley win anyway?

That's the risk, carried by a Flemming who is formidable from the penalty spot, with 3 penalties scored in his last two seasons. But the bet only loses on a Burnley victory: a draw is enough to pass.