I can't speak for Wordpress or Drupal communities, but I've noticed Joomla tends to be made up largely of amateur web developers.
I can't speak for everyone, but from my own experience, those of us that are proficient in PHP and following proper web standards are often so busy, we don't need to look on freelancer.com and similar sites. I've never even had to advertise my services, word of mouth has always been enough.
Oddly, I've noticed this trend too, but from the other side. I built a portfolio, but shockingly few clients request to see past works.
As for finding a freelancer who has already done what you want, how can you expect someone to have already built what you want as a custom extension? If that were likely, wouldn't something already be in the JED?
Unless you meant you can't find someone who has experience writing Joomla extensions, in which case, you're quite justified in demanding experience. My first few extensions were written very poorly.
Just joined in to muse. If I were you, I'd look around for local web development companies, and specifically ask for Joomla development experience. Those online boards are often filled with amateur developers who do not know/follow web standards, accessibility standards, or the API and best practices of Joomla :S
Thanks, helpfull post. I meant the second point, I do not expect someone to have build what I am looking for but 'some' experience with extensions is my requirement
The thing is, I have looked for local companies (I'm in Europe). I have found some and asked for quotes and I just don't get a reply eventhough I can see in the webstats that they have been checking out the site.
And whenever they do reply, they charge consulting like fees. Apparently they either work for the largest companies or they are the 'amateur' developers as you described.