How to connect center of circle with line?

Why dont show point of connection of the circle from the center, to the line when turned on Smart Guides, Snap to Point, Snap to Glyph? What else needs to be turn on? The center of the circle cannot be precisely glued to the line. Why?
In the example it is a simple straight line with angle, I know I can horizontal and vertical align the line and the circle, but what if the line is curved?
