observers standing apart from one another do not see the “same” rainbow. Explain.?

Answer 1

Hi. A rainbow is a visual phenomenon that is caused by light refracting through small droplets in the atmosphere. In another position you would see the rainbow through different droplets.

Answer 2

One sees the light rays that run through the lens of one's eye.
The light from the sun is bent by passing through an array of water droplets to form a rainbow. Because the Sun is the source of light that reaches each of the two observers and because the angular change in the direction of the light rays that reaches one person must be similar to the light rays that reach the other observer the two rainbows must appear to be in different locations.