Maybe 'cause it's more fun to entertain a romantic sort of "Catch-me-if-you-can" ideal than the reality of whatever he may have been running from (to say nothing of the very likely end of the DL agent's career)...
precisely on the first part, sir, and I most certainly hope that no employees are punished for this incident any more than an employee should have been punished for 9/11.
There is a whole lot more to the story than any of us will ever know - there always is with these types of stories.
If an employee was following procedures and the kid managed to bust thru umpteen layers of security, the final one being the boarding door, then you have to ask if there are sufficient and adequate procedures in place.
Who is to say that the kid wasn't smart enough to push his way around another multi-person party was boarding.
Figure out what went wrong, get social service involved, put appropriate checks in process for the future...
Sure, DL or any airline could put up a turnstile type system that permits only one person thru the boarding door for every boarding pass scanned but is that really the image that airlines want to project? And any system can be manipulated, regardless of the company involved, if there is enough criminal intent.
