They do, however, use sun block at somewhere between factor 50 and 100
This (and other posts) highlight some of the common lack of understanding about suncreams and why people would be safer if they just wore UV clothing.
There is no such thing as sun block. If a cream claims to be sun block then it cannot be sold in most of the world (EU, Australia, USA*)
Any SPF claiming higher that 50 offers no more protection so cannot be labelled as such.
No creams are waterproof. The best they can offer is water resistant so creams must be reapplied after about 30 minutes in the water. Again, they cannot be labelled as such.
Reapplying suncream simply replaces cream that has worn off. It does not increase the amount of time you can stay in the sun without burning. If you can stay in the sun for 3 hours with suncream before you start to burn, reapplying after 3 hours will not offer further protection. You have to come out of the sun at that time.
Tanning IS burning. The skin is permanently damaged.
You don't have to tan or burn for permanent damage to be done.
The damage is cumulative over time.
UVB is the main cause of burning but UVA penetrates deeper and causes damage you would not even be aware of.
It's that damage that can become skin cancer decades later.
The chest and back are two of the most common locations for skin cancer to develop (particularly in men)
*Labelling regulations in the EU and Australia have been much stricter for far longer than in the US. The US is still lagging behind in their standards and although the FDA has proposed the same standards as the EU and Aus, they are still faffing around enforcing it. Hence you can still buy a waterproof sunblock SPF100 in the US. It's no better (and is possibly worse), than a water resistant suncream SPF50 bought in the UK.