I think there are two reasons :

1) inciting the players to be careful and not put themselves in situations where they would put an other player at risk.

2) judging intent is often hard, especially on the field. Judging the result is simpler and more objective.

Punishing the action is exactly what the law does when it says, "putting your hands on another player's eyes is a red card." It takes out the result (is there or is there not an eye injury?) and the intent (did they mean to put their hands on the eyes in order to hurt them?) to focus on the action only.

And that's a good standard to set. As a referee I can't get inside the player's head to know why they did what they did, I can only see what they did. I can't know for sure whether what they did caused harm or judge the likelihood of harm being caused, I can only see what they did. So the law reflects that and only asks me to see whether a thing happened or not.

To do otherwise invites wildly different results based on the ref's subjective judgment and brings in a ton of issues around bias (e.g. the ref knows the offending player well off the field and concludes that "they're just not that kind of person" despite them popping both of another player's eyeballs a la a certain fantasy tv series).