Dear, it is the load rating per tyre, and not the rating for combined 04 tyres, or, weight of the persons, luggage, etc.
To give an example, if a tyre can afford at max. 500 Kgs, then 04 tyres will be able to support around 2000 Kgs, which is more than enough, as it covers the weight of the car, as well as passengers, luggage, etc. inside it.
I hope, it helps and guides. Thank you.