Because their model is hosting, not the projects funded there.
They get to rake in provisions on sales of all the burning houses, big difference.
And jokes aside, there's a ton of absolutely legitimate projects going through there like print versions of webcomics, anime etc.
The key really is whether there is something there before the Kickstarter.
If the comic is done, no risk for backers, clear goal, easily achieved and the punishment for non-delivery is loss of fanbase.
If there is a fucking anime studio asking for dosh to make a thing they can't sell to TV, there is already a functional studio with big names and reputation. Real risk of failure, but high incentives for delivering as their paychecks down the line depend on being good for their money.
One asshole has a bit of artwork and rough concepts for an ambitious game that needs a studio to make?
No way that goes well.