On Google Maps, your zoom factor is any real number within a range. On Open Street View, you are stuck using one of several predefined zoom levels (integers 1-20).
To test out, try modifying the "10" in both of the links below: https://www.google.com/maps/@40.7058316,-74.2581905,10z
https://maps.here.com/?map=40.71455,-74.00714,10,normal&x=ep