In some countries atleast they got laws against writing expiration dates more than a year or two later despite some products never expiring or lasting WAY longer than that, helps knowing a bit about such things too..
Also, seems they don't consider the ingredients enough and instead just writing similar dates, for example how long bread lasts is also affected by ingredients and such where some you'll be lucky if they last the week, other kinds lasts two weeks easily, so when they write 8-10 days for all of those.. *Sigh*
(It's not about added chemicals, some kinds just last longer naturally than others, some things can even be used to preserve others..
Extreme example is honey, if you encase something in it, it'll never expire.)