Short job posts are fine for many freelancers. I'm fine with short job posts. I'll bid on jobs with short job descriptions.
A vague job post simply means an hourly contract. So this is fine. If I am hired, then I log time while communicating with the client to figure out what they want.
Clients who don't know what they want? This is fine. I can help them figure that out. All while logging time. On some projects I spend hours with the client just talking about what they need, figuring out what we should do. That is part of the job.
This DOES NOT apply to every type of work, and this does not apply to every freelancer.