Relates to MC-177515
Since obsidian itself requires diamond or netherite to actually drop when broken, these blocks dropping themselves when broken doesn't make sense.
Wooden pickaxe will drop broken iron doors, trapdoors and bars, and heavy weighted pressure plates, cauldrons, anvils and hoppers, despite these being made out of iron
Certain gold and iron based items can be mined with a minimum of a wooden pickaxe
Enchanting tables and ender chests are not in the #dragon_immune tag despite being made of obsidian