You're assuming that everyone views try-out periods in the same negative light that you do. If that were the case, then your conclusion would be right. But not everyone shares your views. Some people prefer to have a try-out period, because it gives them a chance to evaluate the employer.
I'm assuming that the best and the brightest don't have time for a try-out period, because they're busy doing stuff, and don't need one because they can easily get another job.
A try-out can just be on the weekends. I'm sure some people can't even spare any weekends, but there are plenty that can. Many people work on open source in their free time - this isn't all that different.
And true, nobody needs a try-out period - but some want one, in order to help them evaluate their potential employer.
If your assertion is that none of the "best and brightest" want to test out their potential employer, then we'll have to agree to disagree.
