Well and of course because “security” protocols mean that they are secure indeed and not just obscure, like say “compiling my source code into obscure binary format”… “Security” here means that regardless how well you know the protocol, it remains secure.
Unfortunately, “security” in terms of cheating is hard to achieve for any game that uses non-deterministic game logic, like Battlefield or any other game that makes use of advanced physics and needs realtime multiplayer synchronization.
In contrast, games like CandyCrush can be made 100% anti-cheat secure if you exclude bots from the bill.
Then there are of course games like “Go” or 20 years ago also “Chess” that were technically not cheatable, because it would constitute a major technical challenge to create a bot for them that actually can defeat good human players (here only talking about bots, since those games are ridicously easy to make 100% “conventional” cheat proof).