Checkpoint System

So its annoying enough if the bad AI director suddenly spawns four disablers in a ring around the group, two meters away, while fighting a horde or a boss and silent patrols etc. The group wipes five minutes before finishing the map and people who had an absolutely nice playstyle just get nothing out of it and have to restart the map, worst case. Same with the host leaving.
But after this shiny piece of code provided with the newest patch the old problems from V1 are back. I get my group literally deleted, not by the gameplay but by the server which regularly kicks all of them out, starting the hour long process of switiching between bots and players, leaving me completly alone and thus in most cases dead. Even worse, the players who get kicked cant even at least collect their exp. I “leave” games like that where I am not the host as often as I see my group getting wiped. And its not that the game gets “harder” by forced grind due to technical problems (and this software is the pinaccle of it), just more tedious.

So if the game cant provide an at least somewhat stable enviroment but at the same time punishes the player severly for every lag and every second of not being ready for fight, why isnt there something like a checkpoint system that enables a group to try again from a certain point? Because they dont have to grind another hour? Because its difficult to implement? Why?