I don't own a GS, but an R - and since they're similar bikes, I'm allowing myself to reply as well
Had many bikes, many of them bigger than the G310R. Felt the need to try something different. With occupation and children, less time for long road-trips. My use of motorcycles is now mainly for commuting. Makes going to work a little more fun!
Now if I need to find real reasons:
- Cost vs what you get (seemed unbeatable in the 300cc canadian market)
- Longest stock warranty I ever found on a motorcycle (3 years w/ road assist)
- Lower than 400cc means lower plate/insurance cost in my province.
- Relative lightness, ease of use for commuting trough city traffic.
- Shareable with my wife (she did not like hill-climbing on my KTM 690 Enduro (previous bike))
- Owned a bunch a brand but never a BMW, perfect opportunity to try one!
Sharing the garage now, a complete different style of motorcycle: Sherco ST2.9 Trials bike. Nice to have a bike to try all kind of stuff in the woods, when you're tired of riding on pavement following all the rules