So much for the sandbox approach to adventure design. Hrmm, how is this extremely hamfisted punishing the players for not playing the way you want to play? Adding 20 kobolds for good measure? The kobold just happens to "find" the party?
Yeah, no thanks.
Why is my DM decision labelled hamfisting or break the sandbox? You do realize the DM is the arbiter in the sandbox right?
Lets justify the story for the player, since it seems you'd be the player asking "why do monsters have brains?". When my players fall asleep in enemy territory its entirely possible that the kobolds find them, hear them, have ways to detect then (e.g. peepholes or other means). Its entirely possible that they recognize the characters are a powerful force and get reinforcements (friends, allies, a band that was out hunting, things they could summon, resources they wouldnt be able to use without advanced warning, etc).
I try to play my monsters intelligently, in my sandbox the npcs dont wait to be killed, and they go about life if you let them. If my PCs are stupid enough to fall asleep in the hallway the monsters react. I know of late its been fashionable to give the PCs a million hitpoints and let them be the stars every moment, but in my game they have to play smart to win, falling asleep in an occupied lair is generally not smart.
If you prefer endless rooms where monsters are simply waiting, and there are no alarms or defenses, then I suggest you play H1-H3, it seems to be fun for a certain crowd, but not mine. We always hear about other adventurers in D&D, but it seems some players/DMs think monsters have never met them and that this is the first time the Kobolds have been attacked. In my campaign, it generally isnt, if you want to suprise a monster, you actually have to try and do that. Walking in thru the front door and falling asleep, sorry they are prepared for that approach.
There are some situations where the 15 minute work day is applicable, and even warranted, but the vast majority of the situations that I hear it being used is simply bad DMing, and bad adventure design (which I may add is exactly what the article we are talking about stated).