Even in its earliest incarnation, the word "sandbox" was a bit of a misnomer, and there was no set time period for "release". Instead, it was more about establishing trust. With the emphasis today on new and fresh results, we don't see early rankings (after a short honeymoon ranking period) being so crippled any more, but establishing trust is still part of the picture.
If a new site is hoping to rank for very competitive keywords, then it's very unlikely that it will just pop onto the scene with enough trustable backlink juice to compete right away. Churn and burn spammers tend to exploit that early honeymoon period rather than hoping for a long term win.