[badpun]

Maturity is not necessarily a good trait in an employee. Companies hire recent grads specifically because they are immature and will be easier to manipulate. And conversely, companies are often wary of older, mature candidates because such employees won't be easy to manipulate and exploit.

Also, mature people usually come to the conclusion that working a job for someone is pretty sucky way to live, and will either come to terms with it, which often leads to trying to get as little done for as much money as possible (i.e. getting a good deal), or will want to go independent, which will make them unhappy while they're employed. These issues are usually non-existent in the graduate crowd, as they are just amazed that someone is treating them as adults, giving them responsibility and paying for completion of tasks.