It's been the number one complaint on the threads since I can remember, and others that have been here much longer than I have said the same - so it goes way back.
There is only 1 way to prevent it, and wgt does not wish to handle it this way, so you have to find a way around the quitters yourselves.
There are a couple sites outside of wgt that allow you to join leagues, and play with site members who are non-quitters. This one uses a fair handicapping system and gives everyone of every level a chance to win.
http://golfseeker.co.uk/main/
Most members use Skype, either audio equipped or by manual typing, to communicate when setting up matches and to chat while playing. Feel to to stop in and look around or ask questions!