Why not? Many people view it as cool to be able to mow down tons of baddies on their way to the major battle.
It could be a badly done adventure. It could also be that the commoners were bolstered by having high-level adventurers at their back and thus were able to stand up to the monsters that would otherwise have caused them to cower in fear and helplessness.
I don't see a problem here. Or if I do, it's that D&D4e may have decided that "dropping like flies" means that the ogres were killed outright, rather than simply defeated--dead, unconscious, running away, surrendering--like they are in, say, Daggerheart. But I don't know 4e's rules for monsters at 0 hp.
It's like in Lord of the Rings, where whatsisname, Bard, killed Smaug with a single arrow because he managed to hit the one space where there was a missing scale. Nevermind that even if it was some super arrow of slaying, Bard probably wasn't a thief/rogue with a high backstab modifier/sneak attack dice, and nevermind that losing a scale wouldn't actually alter Smaug's AC, and nevermind that an arrow at that range probably wouldn't have the oomph to pierce all the way through the dragon's keel and into his heart, and nevermind that that roll required, like, a natural 20 to hope to hit. We accept all that because it was badass.
And so is the idea of a bunch of commoners being rallied well enough to drive off ogres.
From previous posts you like narrative conceits driving play for more than I do. If I want enemies that they can kill left and right I can still do that in 5e, they just aren't going to be minions.
As far as Bard killing Smaug that was a narrative contrivance. Tolkien needed some way to kill off a legendary dragon.
Different approaches to game design are going to appeal to different people.