In the mobile game it's a MUCH greater percentage of the folks who do it. Maybe it's because of the short timeframe for many of the matches, and they want to get in as many as they can and don't give 2 cents about their opponent or courtesy.
For me the worst time is when people play it through to the end, miss the putt that would tie, then forfeit the match before you can putt for the win, knowing they are screwing you out of the xp. The even cuter ones *cough* send you a message after they forfeit with a F* U* LOL so you know it was deliberate.
If you forfeit it doesn't count as a win or a loss in the monthly stats. You still lose the coins, but some people just do it to be jerks. Yes, you can block them (something I wish you could do in the PC version), but that's another pita and time consuming for you.