Can you tell me in obstructive lung disease, why is expiration difficult and not inspiration?

Airways close down: When you breathe in, you pull open the airways inside your chest. When you exhale, those airways get smaller (especially if you exhale forcefully). Obstructive lung disease causes those airways to get smaller so they are the smallest on exhalation. Snoring is the opposite -- airways outside the chest get smaller when you inhale, so that's why snoring is on inhalation instead of exhalation..