Very simple. I just played an incredibly tilting game (and I mean blood boiling kind of tilting (Enemies trashtalking us constantly and laughing at us for being forced to play without an ADC) because the ADC on our team left right after connecting (Or something like that). He never left the base, and he never bought items. If the player has not taken any action like leaving the base, the game should be eligible for a remake. I understand that you want to give these players, who once connected and might be trying to do this again. the chance to reconnect, but at 5 minutes, you mark any player as 'AFK' and they are no longer able to get the LP for winning.
Why is it impossible to allow for a remake if a player hasn't left base or bought items withing the first 5 minutes of the game.
1. A reconnecting player that takes 5 minutes is a player that holds their team back massively. Not being there for the first 5 min of the game loses you out on multiple levels, gold and tower plating (great addition but this makes coming back after this time impossible). The player nor his team will have fun as the player is too behind and the team, who is forced to do other stuff, cannot make up for his absense.
2. A player that doesn't move or reconnect at all during the game makes the played game a forced 4v5. This is a fact. The player has done nothing; no damage, no wards, no cs, nothing; hasn't even left base or bought his starter item. This is beyond tilting and is in no way shape or form good for the game. It might be frustrating for the enemies to have to play those 5 minutes before ultimately still getting remade, but forcing 5 man to play out a 15+min TEAM game that is essentially lost from minute one, is far and far worse.
A player loses the ability to gain LP after being gone for more than 5 minutes because he didn't reconnect in time. Why in the world does this not allow teammates who are stuck with someone who did not leave base within this time even though he is marked as 'in the game/reconnecting' to remake the game.
Ofcourse the regular 3 minute rule is fine for people who never move, but something as simple as trying to connect once or leaving right after you spawn/disconnecting forces the game to be played out as a 4v5.