The major problem is that the cheapest way to get beads is by the tub. This is - as you might expect - a tub of various colors of beads... all mixed together. Want a black bead? You need to hunt through the tub to find one. Or you can do what we do and manually sort through thousands of beads and group similar colors together in another container.
The only thing you really need to know is - do you think they actually make them in mixed colors? Nah... they make a batch of a gazillion red beads, then blue beads, then green beads, then yellow beads... the tub is just their mix to maximize sales, they know that you'll end up with leftovers and will buy more expensive pure color packs to round it out. It's like how there's a silent conspiracy between hot dog sausages and hot dog bun makers, they avoid matching numbers so you'll always go out shopping more to make use of the leftovers. It's not exactly a coincidence when you end up with a tub full of colors you don't want.