So.. even if I had connection problems once or twice a season, it would be "okay" but all the people who leave games on lower Elo would change their minds asap. Moreover all the people not leaving profit from this change.
In this one paragraph, you listed multiple flaws in your suggestion...
So.. even if I had connection problems once or twice a season, it would be "okay"
How is losing potentially -25*5 = -125 LP be "okay" for a connection problem that you have no control over or you have a family emergency?
all the people who leave games on lower Elo would change their minds asap
What about people who have genuine emergency that is beyond their control or plan? They can't change their minds on having an emergency or something happened that is not planned? How is losing up to -100 LP per game be "okay" when here you are crying about less than -30 LP for having an afk? What about when there is an afk on the other team and you get an easy 5v4 win advantage? Are you "okay" with no gaining any LP off of those games?
Moreover all the people not leaving profit from this change.
And there it is!!! The one keyword that is the major flaw in your suggestion.... "profit". It is "profitable" to have an afk in your team when you are losing. In fact, you are more or less incentivized to create an afk in your team if you are down 5 kills by 10 minutes. You are incentivized to abuse, flame, guilt-trip, threaten your teammate to afk so you don't lose any LP (oh by the way, if you get -0 LP for having afk, do you also gain +0 LP if you do win that hard fought 4v5? Must be a shitty experience to fight for 45 minutes as 4v5 and win...NOTHING). If you also gain +0 LP for winning 4v5, then what's even the point of continue to play the game? Hell, the enemies can even get in on that action, flame, abuse, bm your opponents into afk and you auto-win without having to play the game out since the rest of your opponents have nothing to win or lose.