Mostly because determinism is an all or nothing proposition. Either EVERYTHING in game logic is perfectly deterministic and isolated from everything else, or it pretty much as if nothing was. So if you want to commit to determinism, you have to be constantly vigilant and debugging these maddening types of bugs. Whether this investment is worth it or not is up to each dev.

Sometimes you can find small areas of the game that can be deterministic and worth it. In a basketball game I worked on in the 90s, I designed the ball physics to be deterministic (running at 100hz). The moment the ball left the player hands it ran deterministically; we knew if it was going to hit the shot and if not, where the rebound would go to.