RV3028 VBatt Resistor Value

I was looking at the RV3028 RTC board from Pimoroni and I noticed that the battery is tied to VBackup via a 470k resistor.

I was wondering why the value is so high? The datasheet suggests a value of 100-1000R. I guess it limits the current to a few uA which is still a few order of magnitude higher than the 45nA required by the RV3028. But why 470K? Just a large arbitrary value?