On further inspection, you can actually change the year, but you have to pick a new date in that year.
If you have 30th Jan 2018 selected and you change the year to 2012, it doesn’t automatically choose 30th Jan 2012 (and if you have 30th Jan 2018 selected and you change the month to Feb, it doesn’t have to deal with that ambiguity).
This is the same way that Google Calendar’s Date Picker behaves.
So it’s not broken, although the UX can probably be improved here since it wasn’t obvious to either of us!