It's no longer a metal on metal contact. The two parts are now riding on a film of oil with very little friction and almost no wear.

Same principle as a stepping in a puddle of oil on the floor. Your shoe is now in contact with the oil, not the floor, and you slip over.

Oil creates a film on metal parts that keeps them from touching each other. So when parts slide against each other, they're not rubbing against each other, they're sliding on a thin film of oil.

Try rubbing your fingers together dry then with some oil, you'll notice a huge difference.

thats easy friction is heat liquid cools hot things down.

There's a reason it's called lubrication.