>>36078765Random trainers DO give you money, though. When you black/white out, you resume the game at the last Pokémon Center with only half your money.
This implies 2 things: first, every Pokémon battle between trainers is a wager for half of the cash they have on them at any given time; and second, you as the player character react the same way the NPC’s do when you lose, there’s just no point in showing it happen in the game.
If the NPC’s ran off/disappeared as soon as they lost, you wouldn’t be able to see any text/hints afterwards. But when you lose, why should your voiceless avatar stick around? Are you gonna brag to the computer about how comfy shorts are, before watching an animation where the opponent walks away and then you trudge back to the Pokémon Center?