Social Context: Zombie films are often times too slow and brooding (28 Days Later), too lacking in all departments (Resident Evil) or, in recent years, have become bogged down in their social-political allegory (paging Mr. Romero) that really shouldn’t be there in the first place. Okay, we get it, we’re them, they’re us, we are the living dead shuffling off to our tombstone like office cubicles while we continue to buy things we don’t need and step on who ever gets in our way to the top.We get the social commentary, but its done as a send up in that it pokes fun more at the conventions of the social commentary in other zombie films and not at real life.
http://www.genrebusters.com/film/review_shaun.htm

Historical: 70s: George Romero examined the rise of the new consumer society in his 1978 zombie sequel, Dawn of the Dead;
Millennial horror: There was also something of a revival in British horror film production, with some of the more successful examples including 28 Days Later (2002), Dog Soldiers (2002), Shaun of the Dead (2004) and The Descent (2005), though in the case of the third, with the exception of some considerable gore at the end was more a horror-comedy than a horror film.
http://en.wikipedia.org/wiki/Horror_film#1980s

Economical: Budget : $4,000,000 (estimated)
Opening Weekend:
$3,330,781 (USA) (26 September 2004) (607 Screens)
£1,603,410 (UK) (11 April 2004) (367 Screens)
http://www.imdb.com/title/tt0365748/business

Political: Romero's zombies come partly out of the political turmoil of America in the late 1960s. Zombies became a metaphor for chaos, and an aggressive one.
http://www.smh.com.au/articles/2004/10/06/1096949578716.html

'Dead' movies always reflected a certain something about society at the time: revolution with 'Night…'; the whole consumerist metaphor which is a brilliantly comic aspect of 'Dawn…'; and then with 'Day…' there's a sort of vivisection thing.

“September 11 happened when we were writing and it informed our writing process. We suddenly saw how people reacted in the event of massive social upheaval, and the way that the little problems in your life don't go away. You don't stop being frightened of spiders just because the world's blown up.” Simon Pegg http://www.timeout.com/film/news/631.html