On what criteria does the Palette class pick it's colors?

Question

I understand that the Palette's

Palette.from(bitmap).generate();

method picks by default 16 colors and then finds the best fit for the 6 main color swatches (vibrant, dark vibrant etc.)

I can increase the number of generated colors with

Palette.from(bitmap).maximumColorCount(number).generate();

and it has a higher chance of finding a good color for the different swatches.

But there is no explanation about how these 16+ colors are picked? On what criteria? Why do I get 6 different "main" swatches when I generate different amount of colors, why doesn't it just search for the best fit from the image directly?