I’m not a rules official but I think you will find that “Drop Zone” are not in the rules they are only a Committee agreement to break the rules of golf. In direct violation of rule 1. However, they came about because of TV and temporary immovable obstructions, like stands. It became impractical for players to take the proper relief in accordance with the rules so a “drop zone” was established to solve that problem.
Like many things added for one purpose (like alternative tax methods, ATM) the purpose gets lost and it is used to “speed up play” even if it breaks the rules.
The better question is where in the rules does it say in taking relief from a “water hazard” you can get closer to the hole, and/or on the other side of the hazard.