What you are seeing in the drop down is based on the context of the month/date that you are looking at. When we put the design together, we wanted to allow folks easy access to a range of information that they were most likely to need, The Year list box will dynamically adjust based on the currently selected date and provide one-click into: 2 years prior, current year and the next two years. If you selected a month in 2017 the next time you access the list box it would show 2015-2019.
The two years before and after was a bit of an arbitrary selection, but it seemed like a good balance to keep the list box compact.
Do you frequently find that you need to look beyond 2 years out, or was this just a casual observation?
-Dale