I think the real problem is the specifics.
Like it is really easy to say "leaves get this penalty" and just blanket apply it to anyone who leaves.
But if you try to put in something for people who reconnect then OK should they have to reconnect before X minuses? What is X? Is 5 too low? Maybe 10?
Did they move around after reconnecting? How far did they move? Did they just run in the circle to avoid punishment?
What about how long before the end of the game they reconnected? Did they reconnect just before the end of the game? Did they do that on purposed to avoid punishment? What if they didn't but also didn't have time to walk out of base before the game ended? Do they still get punished?
I could go on and on and on. It is really hard to try to make something "fair" and people will always try to game the system so you risk people abusing it with every rule you add. Much easier to just say "leavers get a penalty" and leave it at that.