For myself, cards are an essential security back up when travelling, in case the truck breaks down, etc.Or maybe they just left credit cards at home and took enough cash to tide them over for the days they'd be away.
Regardless of whether someone found them, they seem to have gone through the wallets, looking for them. But didn't just grab the wallets, as many car thieves do.
It just suggests the idea of someone who took the time to pick through their stuff, carefully removing anything that might have value and leaving/burning what they didn't want. Suggests a partly financial motive, and/or someone who's hard up.