That's one thing I really don't like about some of those posts. They want you to do the very things you would do for a job interview or a paid job, but they want you to do all of this work...for free. It becomes more worrying when they refuse to show their work in return (claiming "idea/art thieves" are rampant) or don't have anything finished themselves.
They want you to put yourself out there for them, for FREE, but aren't willing to do the same.
And I do like to give benefit of the doubt and chalk it up to some of those users being inexperienced and not understanding the implications they're giving. I really want to think that they don't understand yet that there are better ways to ask for help/create collabs.
But sometimes, it's just not the case, and the worse cases are when people get entitled and rude when someone refuses them ("how dare you not work for ME for FREE?!").
It's why I just ignore them most of the time -- being frank, they're sometimes not worth the effort, and I'd rather collab with people who show they can work and work well.