Why cursor pointer size not getting small on Mac OS X sierra?
Please try going to System Preferences->Accesssibility->Display:



Slide the Cursor size knob towards Normal. Does your cursor change size while you are sliding it? If so you can make it smaller that way.

Also, is it possible you have zoomed in or out on the screen itself?

Go to System Preferences->Accessibility->Zoom:



Try turning on Use keyboard shortcuts to zoom, and then use Zoom out to zoom all the way to the normal setting, where you cannot zoom out further.