Explanation:
the question is phrased incorrectly.
the "can" is the problem.
they "can" lie on 3 different planes, even if they are on the same line.
but what 3 points always do in 3-dimensional geometry : they define 1 plane, if they are not on the same line.
it is the minimum of needed information to define a plane : 3 points not on the same line. because they create a triangle, which is a 2- dimensional shape representing its own plane in a 3- dimensional world.
similar to 2-dimensional and 3- dimensional geometry, any 2 points (if they are not identical on the same dot) define 1 line.