Because InDesign uses a proxy of your original images as you place them in InDesign. If you want to view them in Higher Quality then you have to change that.
In InDesign Click View -> Display Performance -> High Quality Display
Shortcut Ctrl + Alt + Cmd + H in Mac
Remember, you don't have to always set your display to a High Quality because the more images you will place in InDesign, you will notice that InDesign becomes sluggish.