Because collinear points are on a single line which makes it impossible to form a triangle!

Can 3 collinear points form a triangle?

If the area of triangle formed by three points is zero, then they are said to be collinear. It means that if three points are collinear, then they cannot form a triangle.

How many collinear points form a triangle?

Three points are collinear if the value of the area of the triangle formed by the three points is zero. Substitute the coordinates of the given three points in the area of triangle formula. If the result for the area of the triangle is zero, then the given points are said to be collinear.