System has called it for the 'lack of financial penalty' aspect. That aside there are some things you can do to address the problem personally:
1. Play with people you can trust to complete games. Make WGT friends of people who finish rounds; conversely don't play repeat offenders, that is do not make them WGT friends.
2. join a country club or start one of your own; in a smaller, controlled population social ostracizing is still an effective tool to enhance behavior.
3. look into one of the non-WGT sites that keep stats and rate players, while actually playing the WGT game. I joined www.wgtls.uk, a site set up by a British fan and members there will not last long if they are quitters. All matches are arranged in a chat room at wgtls.uk first, then set up here at WGT by one of the original challengers. Results are posted by losers and standings are maintained at wgtls.uk
I couldn't find a game there last night and tried the old 'find a random game' here at WGT for the first time in around 6 months, knowing there was some risk. So 4 of us started a 9 hole stroke round ... and the first drop was after one and half holes, The second quitter left after about 6 holes and the game froze, so we 2 remaining players were unable to complete the game.
At that point I remembered why I moved to wgtls.uk !