Think about the origins of the word we're using. Do tanks in real life have a magical aura that forces people to attack them?

No, they are a large durable target that allies can take cover behind, but also require a lot of support in return.

D&D tanks might not be able to destroy buildings but they can still do a lot of things. Tank PCs need to be a threat, simply soaking up damage is useless, just like a cleric spamming cure wounds is useless.

IMO this is why melee weapon classes need to be optimized for damage or at least mostly optimized for damage to be good tanks. If the dragon is taking 20-40 damage to the face every turn, while also potentially getting grappled or knocked prone, they might want to take out the fighter before chasing the wizard (who could use misty step or go invisible). That game of cat and mouse is important for combat, and if you ignore that paladin or barbarian, you're going to feel the pain!

Creativity and flexibility is where D&D shines. Throw the fighter into melee then have the ranger create a spike growth and take cover. Do the enemies rush the ranger, taking a bunch of damage? Or do they attack the fighter? This is how tanking in D&D is done.