It's the whole "you need to volunteer for a year before we'll hire you" hiring method typically seen in low paid positions in the arts, but this time for high paid infosec positions...
Yes, it also is effectively a screen for people with the spare resources to invest in a career without getting paid for it.
But the established folks don't know in advance what exactly that will be... if they did, they'd already be paying someone to do it.
As a new person, there's no better way to demonstrate your ability to make an impact than to just do it.