Without lore, MMOs as we know them wouldn't exist. Lore means different things to different people. Some of us embrace it, some of us let it define who we are and what we do in-game, and some of us ignore it as best we can.
Lore plays an important, central part to any MMO. Central to that lore is the creation of solid, entertaining bad guys – evil, despicable, wicked bad guys that we all take for granted, call out as 'on notice', and sweat blood to chalk up world-first kills for. But you've all been so busy running around taking down bosses left, right and center that it probably never occurred to you that if you're not careful, there's every chance we could run out of bosses to kill.
There's a reason that Blizzard aren't removing old world content from WoW, and it's not because they feel bad that the old bosses don't have anything to do with their time it's because they're scared. Scared of what might happen if there were no more bad guys for us to kill. New content only lasts so long when we've got guilds like Nihilum burning through new content in a matter of days (attracting controversy as they go), and as good as the Blizzard developers are, it's not like they're churning out patch-worthy content every week, is it?