The story goes like this:
"Hey, where are we?" I don't know...
"Who's that?" Huh?
"OH SHIT!! ZOMBIES!" They're coming in...
"We can't escape. Hold them off!" I'll do my best...
Anything else can be imagined to tie in all of the easter eggs and maps and characters. It is human nature to fill in the blanks. The fact remains, most of the info provided is intended to distract you from the fact that you just payed $10 for 1 map, for the third time, and keeps you coming back for more.
Easter Eggs generate interest, youtube videos, forum chat, anticipation of the conclusion, and in the end, that all important reason why they really came out with 3 map packs.....money.