Why are red, blue, yellow only primary colors?

Those are primary colors because if you think about it, you have to mix blue and red to make purple, you have to mix yellow and blue to make green, but lastly, you have to mix red and yellow to make orange. So the reason that they are primary colors is because they make up the secondary colors and in order to make any other color such as pink, teal, fuscia, or even maroon you need to first start off with the primary colors.