DM decides "hey, random encounters to interrupt the player's long rest are a thing, right?".
Let's assume everyone wakes up and isn't surprised or caught napping (which is bad for everyone).
Rogue: "I'm fine, I can sleep in studded leather armor, full AC!".
Ranger: "Me too. Plus I'm sleeping in a tree so monsters can't get me."
Monk: "I mean, I'm always fine."
Barbarian: "I'm down a few points since I can't put on my magic half-plate, but at least I got my unarmored AC."
Druid: "Like my armor ever mattered."
Wizard: "Hey, I think my last Mage Armor is still running, we only got three hours of sleep!".
Cleric, Fighter, and Paladin: "

".
DM: "Aw come on guys, it's realistic! Doesn't this make you feel more immersed in the setting?"