How do rainbows work?

Now I know that rainbows are formed due to refraction of light from the sun hitting raindrops and light waves leave at varying angles between 40-42 degrees or somewhere around there. Also, that they’re round.

What I don’t understand is how it’s consistent, like I assume it’s hitting many raindrops, but all these drops are in different places so why does it still form a nice circle. Furthermore, why isn’t the whole sky a rainbow if it’s raining and thus hitting all the drops. I suspect the angle of the sun is playing a part but I’m not a science man.

Please help me get this thought out of my head.