[Water Warrior 2]

Wide bikes are a refection of their intended purpose due to many factors. Greater sized tanks to increase the range, keep the design flow coherent and match the general appearance. A H-D Sportster is a slim bike with a short range tank. An Ultra model has a larger tank for touring and to match the overall size of the bike.
The GZ has nice lines and fits well with a decent sized tank for long rides.
The one thing I was surprised with and should have realized was the tank on my Vstrom 650. 22 liters will take the bike a long way but it will be a handful till you get used to all the weight so high after a fill up. Cruisers aren't quite as noticeable after a fill up but the Vstrom was an eye opener initially.
Bikes like a Gold Wing have the tank much lower in the body work and are very nimble due to this and some very good overall design.