That is because of a lack of inbound proper links.
Graigslist can add a new city (sub domain) and get high
PR the next
PR update, and its pages will rank for keywords instantly and also have a heavy crawl.
But, all other CL subdomains are linking to them instantly and they are allPR4 or higher indexes from that respective homepage.
There was a recent article about the big companies dominatiating with this exact same method.
You are right that your subdomain will not rank until you beat your competition with links(proper) and proper onpage.
Subdomains are treated as new domains. But i can show you over 50 sites right now with competitive searches at state, national and international levels that are under 6 months old and 1st page in google and yahoo.
If you look at the structure of Cl, you will see over 200 inbound links from the other CL subdomains, and a new city (sub domain) will instantly have clout because they instantly have over 200 PR5 related links. not counting other links.
Go to any state in CL and look for the cities listed as "New" and you will see that they will rank just as well as any other CL subdomain if you post an add with a specific keyword.
How come they are not sandboxed?????
We have already established that a subdomain is a new url from your own post.
The reason your new subdomain did nothing is purely from lack of good links. I would bet money that if you bookmarked a new subdomain in about 100 social bookmarking sites instantly, you would start gaining traffic from
google within a few days as they are links from authority sites and thay are one way links.
Anchor text also affects the rankings.
The sandbox is nothing more than a "theory" just like duplicate content