I agree - and with one of Gandalf's earlier points - much of the problem stems from the winner takes all condition most mp games organised here have.
By late game there are often perfectly viable powers who have no realistic chance of victory. Nearly everyone wants these people to not only keep playing, but to keep playing in their own interests and not simply King make. Maybe it is time to try and add some incentive / reward for doing so?
You can use the Pantheon system - which I must say I like the sound of
Or have more games that allow allied victories. Or vassals.
Or we could all revisit the idea of scoring games/creating a league as was suggested a few months ago? That would reward people who stay in or hold VPs at the end. Obviously depending on the complexity of the scoring method used. If part of the aim of the league was to encourage/reward people to both stay in and fight to the end then the idea might get more support than it gathered last time.